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, CYLINDER AIR PRESSURE ABOVE 6 PSI COULD NOT BE MAINTAINED IN NR 2 CYLINDER. AIR WAS FELT ESCAPING FROM THE INDUCTION AIRBOX. MECHANIC TAPPED ON INTAKE VALVE WITH A DRIFT. SUBSEQUENT COMPRESSION CHECKS FAILED AS WELL. CYLINDER REMOVED. FOUND EXHAUST VALVE CORRODED AND PITTED BEYOND LIMITS. INTAKE AND EXHAUST VALVES WERE RE-SEATED AND CYLINDER BENCH CHECKED.