As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT (2,500 ER PM AND 37 MAP) ENGINE BACKFIRED AND FAILED. AIRCRAFT WAS LANDED W/O FURTHER INCIDENT OR DAMAGE. INSPECTION REVEALED FAILURE OF PHENOLIC GEAR INSIDE MAGNETO. GEAR IS LUBRICATED DURING O/H BUT WAS DRY. RECOMMENDED EVALUATION OF TYPE OIL USED DURING O/H LUBRICATION AND PROCEDURE FOR RE-LUBRICATING IN THE FIELD. (K)