As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED LEFT ENGINE LEFT MAGNETO WAS 'DEAD' ON RUN-UP. REMOVED MAGNETO AND OPENED UP FOR INSPECTION. FOUND INTERNAL DAMAGE - MATERIAL BEING WORN AWAY BY ROTATING MAGNET. FURTHER DISASSEMBLY REVEALED DRIVE END BEARING P/N M3006 BALL RETAINER CAGE AND GREASE SEAL GONE - BEARING WAS DRY WHICH MAY HAVE LEAD TO FAILURE. NEW MAGNETO INSTALLED ON AIRCRAFT AND RETURNED TO SERVICE.