What was found
HYRAULIC QUANTITY DROPPED AFTER TAKEOFF, TO 0 IN NORMAL. CONTINUED TO DROP SLOWLY DURING FLIGHT. EMERGENCY CHECKLIST WAS FOLLOWED UP TO ABNORMAL PROCEDURES. HYDRAULIC QUANTITY REMAINED ABOVE STAND-PIPE. LANDING WAS UNEVENTFUL. FOUND NR 3 ENGINE DRIVEN HYDRAULIC PUMP LEAKING AT PRESSURE LINE. REPLACED O-RING AND CHECKED SYSTEM IAW DC8 MM, NO LEAKS NOTED.