As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A ROUTINE 100-HOUR INSPECTION, THE NR 4 CYLINDER WAS FOUND TO HAVE LEAKAGE PAST THE EXHAUST VALVE. FURTHER INVESTIGATION REVEALED A WORN OUT EXHAUST VALVE GUIDE. REPLACING THE GUIDE AND RE-FACING THE EXHAUST VALVE RESOLVED THE PROBLEM. SUBMITTER SUGGESTED POSSIBLE CAUSE AS DEFECTIVE PARTS OR ASSEMBLY PROCESS FROM THE FACTORY.