As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT ANNUAL INSPECTION, NOTICED CORROSION ON THE MAIN ELECTRICAL CONTACTOR AND THE STARTER RELAY. SUSPECT THE BATTERY WAS VENTING OUT BY THE CABLES. CHECKING THE BATERY BOX VENT, IT WAS FILLED WITH MUD DAUBER LARVA. THIS AIRCRAFT HAD ACCUMULATED 36 HOURS SINCE THE LAST OVERHAUL.