What was found
DURING FLT, PILOT NOTICED A VERY SLIGHT RPM DROP AND SLIGHT ROUGHNESS. UPON LANDING A GROUND RUN WAS PERFORMED AND WHEN THE IGNITION SWITCH WAS SELECTED TO RT MAG, ENGINE DIED OFF BEFORE SELECTING BACK TO LT OR BOTH. WHEN COWLS WERE REMOVED IT WAS EVIDENT THAT RT MAG HAD SEPARATED FROM ATTACH FLANGE AND WAS LAYING JUST FWD OF ITS ATTACHMENT POINT. UPON INSPECTION OF MAG IT APPEARS THAT IMPULSE COUPLING HAD FAILED INTERNALLY AND THROUGH ROTATION AND CENTRIFICAL FORCE HAD WORN AWAY THE CASING OF THE MAG TO THE POINT OF SEPARATION. MAG WAS REPLACED WITH A NEW UNIT, THE ACCY CASE GEARS WERE VISUALLY INSPECTED, AND THE OIL AND FILTER WERE CHANGED AT THAT TIME AND AGAIN 3 HOURS LATER.