diff --git a/src/components/three/gameplay/RepairObjectModel.tsx b/src/components/three/gameplay/RepairObjectModel.tsx
index cb678c0..e8671c8 100644
--- a/src/components/three/gameplay/RepairObjectModel.tsx
+++ b/src/components/three/gameplay/RepairObjectModel.tsx
@@ -8,6 +8,7 @@ import { toVector3Scale } from "@/utils/three/scale";
 interface RepairObjectModelProps extends ModelTransformProps {
   label: string;
   modelPath: string;
+  ghosted?: boolean;
 }
 
 interface RepairObjectModelBoundaryProps extends RepairObjectModelProps {
@@ -73,6 +74,7 @@ export function RepairObjectModel({
   position = [0, 0, 0],
   rotation = [0, 0, 0],
   scale = 1,
+  ghosted = false,
 }: RepairObjectModelProps): React.JSX.Element {
   return (
     <RepairObjectModelBoundary
@@ -87,6 +89,7 @@ export function RepairObjectModel({
         position={position}
         rotation={rotation}
         scale={scale}
+        opacity={ghosted ? 0.35 : 1}
       />
     </RepairObjectModelBoundary>
   );
diff --git a/src/components/three/gameplay/RepairRepairingStep.tsx b/src/components/three/gameplay/RepairRepairingStep.tsx
index 27d20de..471f71d 100644
--- a/src/components/three/gameplay/RepairRepairingStep.tsx
+++ b/src/components/three/gameplay/RepairRepairingStep.tsx
@@ -81,6 +81,9 @@ export function RepairRepairingStep({
   const [depositedBrokenPartIds, setDepositedBrokenPartIds] = useState<
     Record<string, boolean>
   >({});
+  const [heldPartByLockGroup, setHeldPartByLockGroup] = useState<
+    Record<string, string>
+  >({});
   const [showBlockedInstallFeedback, setShowBlockedInstallFeedback] =
     useState(false);
   const replacementParts = getReplacementParts(config);
@@ -183,6 +186,24 @@ export function RepairRepairingStep({
     });
   }
 
+  function handleReplacementGrabChange(
+    part: RepairMissionPartConfig,
+    held: boolean,
+  ): void {
+    if (!part.caseLockGroup) return;
+    const group = part.caseLockGroup;
+    setHeldPartByLockGroup((current) => {
+      if (held) {
+        if (current[group] === part.id) return current;
+        return { ...current, [group]: part.id };
+      }
+      if (current[group] !== part.id) return current;
+      const next = { ...current };
+      delete next[group];
+      return next;
+    });
+  }
+
   return (
     <group ref={groupRef}>
       <RepairInstallTarget
@@ -211,6 +232,10 @@ export function RepairRepairingStep({
           config.requiredReplacementPartIds,
           isPlaced,
         );
+        const lockedByOther =
+          part.caseLockGroup !== undefined &&
+          heldPartByLockGroup[part.caseLockGroup] !== undefined &&
+          heldPartByLockGroup[part.caseLockGroup] !== part.id;
 
         return (
           <GrabbableObject
@@ -218,7 +243,11 @@ export function RepairRepairingStep({
             position={placeholderPosition}
             colliders="ball"
             handControlled
+            disabled={lockedByOther}
             label={`Prendre ${part.label}`}
+            onGrabChange={(held) => {
+              handleReplacementGrabChange(part, held);
+            }}
             onPositionChange={(position) => {
               handleReplacementPosition(part.id, position);
             }}
@@ -234,6 +263,7 @@ export function RepairRepairingStep({
                 label={part.label}
                 modelPath={part.modelPath ?? config.modelPath}
                 scale={0.36}
+                ghosted={lockedByOther}
               />
               <RepairPartPlacementFeedback state={feedbackState} />
             </group>
diff --git a/src/components/three/interaction/GrabbableObject.tsx b/src/components/three/interaction/GrabbableObject.tsx
index 62821da..f0cc054 100644
--- a/src/components/three/interaction/GrabbableObject.tsx
+++ b/src/components/three/interaction/GrabbableObject.tsx
@@ -34,6 +34,8 @@ interface GrabbableObjectProps {
   colliders?: ColliderShape;
   label?: string;
   handControlled?: boolean;
+  disabled?: boolean;
+  onGrabChange?: (held: boolean) => void;
   onPositionChange?: (position: THREE.Vector3) => void;
   onSnap?: (position: THREE.Vector3) => void;
   snapDuration?: number;
@@ -131,6 +133,8 @@ export function GrabbableObject({
   colliders = GRAB_DEFAULT_COLLIDERS,
   label = GRAB_DEFAULT_LABEL,
   handControlled = false,
+  disabled = false,
+  onGrabChange,
   onPositionChange,
   onSnap,
   snapDuration = 0.25,
@@ -152,6 +156,19 @@ export function GrabbableObject({
     };
   }, []);
 
+  useEffect(() => {
+    if (!disabled) return;
+    if (isHolding.current) {
+      isHolding.current = false;
+      onGrabChange?.(false);
+    }
+    if (isHandHolding.current) {
+      isHandHolding.current = false;
+      InteractionManager.getInstance().setHandHolding(false);
+      onGrabChange?.(false);
+    }
+  }, [disabled, onGrabChange]);
+
   function snapToNearestTarget(): void {
     const body = rbRef.current;
     if (!body || snapTargets.length === 0 || snapRadius <= 0) return;
@@ -242,14 +259,16 @@ export function GrabbableObject({
   useFrame(() => {
     if (!rbRef.current) return;
 
-    const fistHand = handControlled
-      ? hands.find((hand) => hand.isFist)
-      : undefined;
-
     const t = rbRef.current.translation();
     _currentPos.set(t.x, t.y, t.z);
     onPositionChange?.(_currentPos);
 
+    if (disabled) return;
+
+    const fistHand = handControlled
+      ? hands.find((hand) => hand.isFist)
+      : undefined;
+
     if (fistHand) {
       const handCenter = getHandCenterPoint(fistHand);
 
@@ -267,15 +286,20 @@ export function GrabbableObject({
           ? getHandHit(groupRef.current, camera, _cameraPos, handCenter)
           : null;
 
-        isHandHolding.current = Boolean(hit);
-        InteractionManager.getInstance().setHandHolding(isHandHolding.current);
+        const hadHit = Boolean(hit);
+        if (hadHit) {
+          isHandHolding.current = true;
+          InteractionManager.getInstance().setHandHolding(true);
+          onGrabChange?.(true);
+        }
       }
     } else {
       if (isHandHolding.current) {
         snapToNearestTarget();
+        isHandHolding.current = false;
+        InteractionManager.getInstance().setHandHolding(false);
+        onGrabChange?.(false);
       }
-      isHandHolding.current = false;
-      InteractionManager.getInstance().setHandHolding(false);
     }
 
     if (!isHolding.current && !isHandHolding.current) return;
@@ -311,35 +335,41 @@ export function GrabbableObject({
         position={position}
       >
         <group ref={groupRef}>
-          <InteractableObject
-            kind="grab"
-            label={label}
-            position={position}
-            bodyRef={rbRef}
-            onPress={() => {
-              isHolding.current = true;
-            }}
-            onRelease={() => {
-              isHolding.current = false;
-              snapToNearestTarget();
-              if (
-                !rbRef.current ||
-                grabDebugParams.throwBoost === GRAB_THROW_BOOST_DEFAULT
-              )
-                return;
-              const v = rbRef.current.linvel();
-              rbRef.current.setLinvel(
-                {
-                  x: v.x * grabDebugParams.throwBoost,
-                  y: v.y * grabDebugParams.throwBoost,
-                  z: v.z * grabDebugParams.throwBoost,
-                },
-                true,
-              );
-            }}
-          >
-            {children}
-          </InteractableObject>
+          {disabled ? (
+            children
+          ) : (
+            <InteractableObject
+              kind="grab"
+              label={label}
+              position={position}
+              bodyRef={rbRef}
+              onPress={() => {
+                isHolding.current = true;
+                onGrabChange?.(true);
+              }}
+              onRelease={() => {
+                isHolding.current = false;
+                onGrabChange?.(false);
+                snapToNearestTarget();
+                if (
+                  !rbRef.current ||
+                  grabDebugParams.throwBoost === GRAB_THROW_BOOST_DEFAULT
+                )
+                  return;
+                const v = rbRef.current.linvel();
+                rbRef.current.setLinvel(
+                  {
+                    x: v.x * grabDebugParams.throwBoost,
+                    y: v.y * grabDebugParams.throwBoost,
+                    z: v.z * grabDebugParams.throwBoost,
+                  },
+                  true,
+                );
+              }}
+            >
+              {children}
+            </InteractableObject>
+          )}
         </group>
       </RigidBody>
     </group>
diff --git a/src/components/three/models/SimpleModel.tsx b/src/components/three/models/SimpleModel.tsx
index 0122940..7d0e0b1 100644
--- a/src/components/three/models/SimpleModel.tsx
+++ b/src/components/three/models/SimpleModel.tsx
@@ -17,10 +17,29 @@ function applyShadowSettings(
   });
 }
 
+function applyOpacity(object: THREE.Object3D, opacity: number): void {
+  object.traverse((child) => {
+    if (!(child instanceof THREE.Mesh)) return;
+
+    const materials = Array.isArray(child.material)
+      ? child.material
+      : [child.material];
+
+    materials.forEach((material) => {
+      if (!(material instanceof THREE.Material)) return;
+      material.transparent = opacity < 1;
+      material.opacity = opacity;
+      material.depthWrite = opacity >= 1;
+      material.needsUpdate = true;
+    });
+  });
+}
+
 interface SimpleModelConfig extends ModelTransformProps {
   modelPath: string;
   castShadow?: boolean;
   receiveShadow?: boolean;
+  opacity?: number;
 }
 
 interface SimpleModelProps extends SimpleModelConfig {
@@ -34,6 +53,7 @@ export function SimpleModel({
   scale = 1,
   castShadow = true,
   receiveShadow = true,
+  opacity = 1,
   children,
 }: SimpleModelProps): React.JSX.Element {
   const { scene } = useLoggedGLTF(modelPath, {
@@ -48,6 +68,10 @@ export function SimpleModel({
     applyShadowSettings(model, castShadow, receiveShadow);
   }, [castShadow, model, receiveShadow]);
 
+  useEffect(() => {
+    applyOpacity(model, opacity);
+  }, [model, opacity]);
+
   const parsedScale =
     typeof scale === "number" ? ([scale, scale, scale] as Vector3Tuple) : scale;