As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE ROTOR GEAR LOOSENED ON ROTOR SHAFT DUE TO NORMAL WEAR AND THERMAL CYCLING. THE GEAR THEN RUBBED THE DISTRIBUTOR BLOCK GENERATING NYLON PARTICLES THAT CONTAMINATED THE CONTACTS. THIS RENDERED THE MAGNETO INOPERATIVE. THIS ROTOR GEAR IS A PRESS FIT ON THE ROTOR AND NO MECHANICAL RETENSION IS USED.