As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A ROUTINE COMPRESSION CHECK, THE EXHAUST VALVE WAS FOUND LEAKING ON THE NR 1 CYLINDER. THE REMOVED CYLINDER HAD A WORN OUT EXHAUST VALVE AND GUIDE. SUBMITTER SUGGESTED POSSIBLE CAUSE AS DEFECTIVE PARTS OR ASSY PROCESS AT THE FACTORY.