As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WITHIN THE LAST 3 TO 3.5 HOURS OF FLIGHT, THE PILOT NOTED THE ENGINES WERE RUNNING ROUGH AND FLEW TO OUR FACILITY FOR DISCOVERED THAT THE INTAKE VALVE KEEPER KEYS WERE BROKEN, THE NR 6 CYLINDER HAD A STUCK EXHAUST VALVE. THE PILOT REPORTED HAVE THE NR 6 CYLINDER REPLACED WITH A REMANUFACTURED UNIT AT ANOTHER FACILITY FAIRLY RECENTLY. ON THE LT ENGINE, THE NR 4 INTAKE VALVE STEM WAS DISCOVERED TO BE BROKEN.