What was found
(CAN) DURING CRUISE, 42 MINUTES AFTER TAKEOFF, THE NR 1 ENGINE OIL QUANTITY WAS READ AT 1.75 GALLONS. THE OIL LEVEL HAD BEEN SERVICED TO 4.0 GALLONS PRIOR TO DEPARTURE. DURING THE NEXT 5 MINUTES, THE OIL QUANTITY DECREASED TO 1.25 GALLONS. THE NR 1 ENGINE WAS SHUT DOWN AND THE AIRCRAFT RETURNED TO ITS DEPARTURE POINT. POST-FLIGHT INVESTIGATION FOUND THE BEARING/SLINGER RING FOR THE DRIVE SHAFT TO WHICH THE STARTER CONNECTS HAD SHIFTED IN ITS HOUSING, ALLOWING ENGINE OIL TO FLOOD THE CAVITY AND VENT OVERBOARD. THE ENGINE ACCESSORY GEARBOX IS BEING REPLACED.