As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ROUGH MAGNETO ENCOUNTERED ON RUN-UP MAGNETO CHECK. INSPECTION FOUND FAILED ROTOR AT TRAILING FINGER TOWER WHICH CAUSED ROTOR TO LOCK UP IN TOWER, SHEARING DRIVE GEARS ON PLASTIC GEAR BENDING DRIVE COUPLING TIN, AND DESTROYING DRIVE CUSHIONS AND DEFORMING END OF GEAR DRIVE SHAFT. SUSPECT CAUSE IS AGE OF PLASTIC GEAR.