As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ANNUAL INSPECTION, OIL WAS FOUND LEAKING NEAR BOTTOM OF ROCKER COVERS. THE LEAK WAS TRACKED TO THE CASTING LINE BETWEEN THE VALVE GUIDES IN THE FIN AREA. LOCATION OF THE PROBLEM IS THE SAME ON ALL 4 CYLINDERS. LEAK SEEMED TO BE CAUSED BY POROSITY IN CASTING LINE. (X)