What was found
(CAN) LEFT HAND LANDING GEAR HOOK FAILED TO MOVE INTO POSITION ON RETRACTION AFTER TAKEOFF. INVESTIGATION FOUND ACCUMULATED DIRT AND RUST ON THE UPLOCK ROD, TELESCOPIC END, UNDER THE DUST BOOT, CAUSING SLUGGISH OPERATION OF UPLOCK HOOK. IT IS TO BE NOTED THAT CLEANING AND LUBRICATION IS REQUIRED AFTER EACH LANDING GEAR AND WHEELWELL WASHING.