What was found
PILOT REPORTED DROP IN RIGHT ENGINE OIL PRESSURE DURING CLIMB THROUGH 10,000 FT AFTER DEPARTURE FROM FSD. NO EMERGENCY WAS DECLARED. PILOT RETURNED AIRCRAFT TO FSD WHERE MAINTENANCE DISCOVERED A FAILED PROPELLER LOCK LIMIT SWITCH GASKET; CAUSING THE LOSS OF ENGINE OIL. CORRECTIVE ACTION: PROPELLER LOCK LIMIT SWITCH GASKET WAS REPLACED ENGINE RUNS WERE PERFORMED WITH UNSATISFACTORY RESULTS. RIGHT ENGINE WAS REPLACED, GROUND RUNS COMPLETED, AIRCRAFT RETURNED TO SERVICE.