What was found
EN ROUTE, THE RT ENGINE SHUTDOWN ON ITS OWN, PILOT FEATHERED THE ENGINE AND LANDED, NO PROBLEM. MAINT.CHECKED FOR WATER IN FUEL (NONE FOUND),CHECKED OIL FILTER (NOTHING FOUND),CHANGED PLUGS FOR PRECAUTIONARY MEASURES. TRIED TO RUN ENGINE COULD ONLY GET 800RPM, CHECKED UNFEATHERING ACCUMULATOR IT WAS OK, BUT DID FIND OIL IN THE AIR SIDE OF THE PROP DOME, SWAPPED PROP FROM LT ENGINE, RT ENG RAN FINE. INSTALLED OVHL PROP ON LT ENGINE. GOING TO DO A TEST FLT ON AIRCRAFT BEFORE RELEASING FOR 135 FLT. MECHANIC COULD NOT FIND ANY REASON FOR ENGINE TO COMPLETELY SHUT DOWN IN FLT, FULL POWER GROUND NORMAL.