What was found
(CAN) DURING INSPECTION, AN OIL LEAK WAS DISCOVERED ON THE RT ENGINE CYLINDER POSITION NR 2. UPON INVESTIGATION AND RECTIFICATION, THE MAINTENANCE CREW WAS ATTEMPTING TO REPLACE THE O-RINGS ON THE EXHAUST ROCKER ARM RETAINING BOLT. THE RETAINING NUT AND COTTER PIN CAME OFF AS A COMPLETE UNIT. IT WAS NOTED THAT THE BOLT HAD SHEARED AT THE FIRST ROW OF THREADS. THE BOLT WAS REPLACED AND THE AIRCRAFT WAS RETURNED TO SERVICE.