What was found
(CAN) SHORTLY AFTER TAKEOFF, CREW NOTICED SYS (A) HYDR INDICATED ZERO QTY. CREW DECLARED AN EMERGENCY, ASKED FOR A RETURN TO AIRPORT. CREW REQUESTED A FUEL DUMP, THIS WAS APPROVED BY ATC. AFTER FUEL DUMPING WAS COMPLETED AC RETURNED AIRPORT FOR ARRIVALS ILS 29. AC LANDED SAFELY AND WAS TOWED TO RAMP. INSP WAS ACCOMPLISHED. CAUSE OF HYDR FAILURE WAS FAILED O-RING EXTRUDING FROM IB FLAP PWR UNIT HYDR MOTOR. MOTOR ASSY AND O-RING REPLACED, (A) SYSTEM FILTERS REMOVED, INSPECTED FOR METAL. FILTERS FOUND CLEAN. OB MOTOR WAS REMOVED, INSPECTED, FOUND SERVICEABLE. IAW MM FILTERS TO BE REINSPECTED AFTER 200 HOURS. AC HYDR SYS SERVICED, AC WAS RETURNED TO SERVICE. (TC NR 20060208009)