What was found
AFTER TAKEOFF, THE CREW OBSERVED FLUCTUATING REDUCTION GEARBOX OIL PRESSURE ON THE LT ENGINE WITH A CORRESPONDING LOSS OF OIL QUANTITY. THE CREW PERFORMED AND ENGINE SHUTDOWN AND RETURNED, WHERE THEY LANDED UNEVENTFULLY. MAINTENANCE DETERMINED THAT AN O-RING SEAL HAD BEEN (ROLLED) DURING THE INSTALLATION OF A RECENTLY INSTALLED STARTER. THE O-RING WAS REPLACED AND THE AIRCRAFT RETURNED TO SERVICE.