As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED MAG FAILURE, LEFT MAG DROPPED 600 RPM. WHEN TAXING BACK TO RAMP, HIGH PITCHED HUMMING OCCURRED, GOT LOUDER WITH HIGHER RPM. REMOVED RIGHT MAGNETO AND DISCOVERED THAT THE MAGNETO IMPULSE COUPLING RIVET FAILED AND MAGNETO SEIZED. THERE WAS DAMAGE TO ENGINE GEAR TRAIN. CHECKED LEFT MAGNETO IMPULSE COUPLING FLYWEIGHT RIVETS AND FOUND WERE LOOSE.