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 THE RPM. ACFT GROUNDED. MECHANIC PERFORMED A COMPRESSION CHECK ON ENGINE AND FOUND THE NR 6 CYLINDER HAD A COMPRESSION OF 42/80 AND THE AIR LEAKAGE WAS PASSING THE EXHAUST VALVE. FURTHER INSPECTION IAW SB 388C REVEALED THAT THE EXHAUST VALVE TO GUIDE CLEARANCE WAS .032", WHICH EXCEEDS THE MAXIMUM CLEARANCE (.030") ALLOWED IAW PARA 12. CYLINDER REMOVED FROM SERVICE.