As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RT MAGNETO INSPECTED DUE TO FAILURE OF LT MAGNETO. UPON INTERNAL VISUAL INSP, FOUND CRACKED MAGNETO SHAFT BELOW DRIVE GEAR. ALUMINUM MAGNET CASTING FAILED AT STEEL SHAFT MATING JOINT. ROTATION OF STEEL SHAFT IN ALUMINUM CASTING WAS IMMINENT. MAGNETO WAS "FACTORY NEW" WITH 350.9 HOURS TT AND HAS NOT BEEN OPENED PRIOR TO THIS EVENT. A REPLACEMENT "FACTORY NEW" MAGNETO OF THE SAME TYPE WAS INSTALLED TO RESOLVE THE PROBLEM.