What was found
(CAN) AIRCRAFT MASTER CAUTION LIGHT ' NR 2 OIL PRESSURE ' ILLUMINATED IN CRUISE. THE OIL PRESSURE GAUGE WAS AT 50 PSI AND THE NR 2 ENGINE TORQUE METER GAUGE WAS READING LOW AND FLUCTUATING. THE FLIGHT CREW BROUGHT THE ENGINE TO FLIGHT IDLE AND DID A PRECAUTIONARY LANDING AT VANCOUVER AIRPORT. THE TORQUE SYSTEM AND ENGINE OIL SYSTEM WERE INSPECTED AND THE OIL FILTER/ REGULATOR VALVE ASSY WAS CHANGED. A GROUND RUN AND TEST FLIGHT WERE SATISFACTORY. APPROX. 1 HR LATER SAME HAPPENED AGAIN. THE ENGINE GEAR BOX WITH THE SUSPECT PUMP IN IT WERE REMOVED AND A SERVICEABLE GEAR BOX WAS INSTALLED GROUND RUNS AND TEST FLIGHTS CARRIED OUT AND THE AIRCRAFT WAS RETURNED TO SERVICE.