As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE LT ENGINE BEGAN TO RUN ROUGH. MAINTENANCE TRACED PROBLEM TO LT MAG. UPON OPENING THE MAGNETO, DISCOVERED THE DISTRIBUTOR GEAR MISSING 98 PERCENT OF ITS TEETH WITH MANY BROKEN PIECES AND SHAVINGS INSIDE THE MAG. THE DISTRIBUTOR GEAR BUSHING IS LOOSE INSIDE THE DISTRIBUTOR BLOCK. THIS MAGNETO OVERHAULED.