As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PROPELLER AND ENGINE PULSE CAVITATION IN FLIGHT. SIGNIFICANT OIL LEAK ON GROUND. HAD 19 INCHES MANIFOLD PRESSURE, 2100 RPM WHEN SLOWLY ADVANCING RPM. ACFT GROUNDED. MECHANIC PERFORMED A COMPRESSION CHECK ON ENGINE AND FOUND NR 4 CYLINDER HAD AN ACCEPTABLE COMPRESSION OF 74/80. FURTHER INSPECTION IAW SB388C REVEALED THAT THE EXHAUST VALVE TO GUIDE CLEARANCE WAS .032", WHICH EXCEEDS THE MAXIMUM CLEARANCE (.030") ALLOWED IAW PARAGRAPH 12. CYLINDER REMOVED FROM SERVICE.