What was found
BOS - FLT 3110 - WHILE AT CRUISE, CREW NOTICED THE RT ENGINE OIL PRESSURE WAS FLUCTUATING BETWEEN 70-80 PSI. THE OIL PRESSURE STARTED A SLOW DROP TO BETWEEN 40-50 PSI AT WHICH POINT THE ENGINE WAS SHUT DOWN BY THE CREW. AIRCRAFT CONTINUED TO BOS AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE STARTER/GENERATOR DRIVE O-RING CUT WHICH ALLOWED ENGINE OIL TO LEAK OUT CAUSING THE PRESSURE TO DROP. THE O-RING WAS REPLACED AND OIL SYSTEM SERVICED. GROUND RAN ENGINE PER GE PROCEDURES ALL CHECKED GOOD. AIRCRAFT WAS RETURNED TO SERVICE. (M)