What was found
(CAN) DURING APPROACH WHEN FLAPS SELECTED, THE FLAP DRIVE CAUTION LIGHT CAME ON. POST-LANDING INSPECTION FOUND THE FLAP PRIMARY TORQUE DRIVE SHAFT INTERNAL SPLINE WORN OUT. IT ALSO HAD RED RUST AND WAS DRY, WITH NO LUBRICATION EVIDENT. DEHAV TASK CALLS FOR LUBE OF SPLINE EVERY 8,000 HOURS OR 9000 CY. AIRCRAFT HAD 5,286 HOURS AND 7183 CY SINCE TASK LAST ACCOMPLISHED.