What was found
(CAN) AT 16,000 FEET, OIL PRESSURE ON NR 1 ENGINE GRADUALLY DROPPED. PRECAUTIONARY SHUT DOWN WAS CARRIED OUT ON NR 1 ENGINE. POST-FLIGHT INSPECTION FOUND THE SOURCE OF THE OIL LEAK TO BE A LEAKING GARLOCK SEAL ON THE ENGINE DRIVEN HYDRAULIC PUMP. GARLOCK CARRIED SEAL, O-RING, AND ENGINE DRIVEN PUMP SHAFT, O-RINGS WERE REPLACED. OIL SERVICED, ENGINE GROUND RUN, NO FURTHER LEAKS WERE FOUND. THE AIRCRAFT WAS RETURNED TO SERVICE.