What was found
(CAN) APPROXIMATELY .5 HOUR INTO A FLIGHT, THE LT ENGINE LOW OIL PRESSURE LIGHT CAME ON AND THIS WAS CONFIRMED BY THE GAUGE READING. THE LT ENGINE WAS SHUTDOWN IN FLIGHT AND THE ACFT RETURNED WITHOUT INCIDENT TO AIRPORT. AFTER INVESTIGATION BY THE ENGINEER IT WAS FOUND THAT THE ENGINE HAD AN OIL LEAK COMING FROM THE PROPELLER PITCH CONTROL UNIT MOUNTING PAD ON THE BACK OF THE REDUCTION GEAR BOX. THE MOUNTING PAD WAS REMOVED AND AN O-RING ON 1 OF THE TRANSFER TUBES WAS FOUND TO BE BADLY DETERIORATED.