What was found
DTW - ON APPROACH, LOSS OF LEFT HYDRAULIC FLUID AND PRESSURE OCCURRED AFTER AUXILIARY AND ALTERNATE PUMPS WERE ACTIVATED. FOLLOWED COCKPIT OPERATING PROCEDURES AND LANDED WITHOUT INCIDENT. FOUND LEFT ENGINE HYDRAULIC PUMP LEAKING FROM SCREW HOLE AT BOTTOM OF PUMP. HOLE THREADS WERE STRIPPED WITH SCREW HANGING FROM SAFETY WIRE. REPLACED THE LEFT ENGINE HYDRAULIC PUMP AND OPERATIONAL CHECK OK. AIRCRAFT RETURNED TO SERVICE.