As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING AN OIL CHANGE, TWO RIVET HEADS (AN470) WERE FOUND IN THE OIL SUCTION SCREEN. THE ENGINE WAS REMOVED AND THE OIL SUMP PULLED OFF. TWO RIVET HEADS WERE MISSING FROM THE OIL SUMP BAFFLE. THESE ARE MS20470AD4-4 RIVETS. THE HOLES ON THE DRIVEN SIDE APPEARED TO BE COUNTERSUNK OR EXCESSIVELY DEBURRED, WHICH GAVE LITTLE BEARING SURFACE FOR THE RIVET HEAD. LYCOMING SB489B REFERS TO THESE RIVETS AND THEIR REPLACEMENT.