As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER COMPLETION OF THE ANNUAL INSPECTION, WE PERFORMED A POST INSPECTION RUN. DURING IDLE WE CHECKED EACH MAGNETO AND FOUND THAT THE ENGINE RAN SIGNIFICANTLY ROUGHER ON THE LEFT MAGNETO THAN THE RIGHT MAGNETO. AT HIGHER RPM OPERATION WAS NORMAL. REMOVED LEFT MAGNETO AND OPENED FOR INSPECTION. IT WAS FOUND THAT THE MAGNETO OIL SEAL FAILED. THIS MAGNETO IS NEW WITH ONLY 105 HOURS SINCE INSTALLATION.