As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CYLINDER WAS REMOVED FOR LEAKING EXHAUST VALVE BY CUSTOMER. UPON DISASSEMBLY AND REMOVAL OF LOWER VALVE SPRING RETAINER, THE GUIDE WAS FOUND TO BE IN TWO PIECES. THE LOWER HALF WAS STILL IN THE CYLINDER HEAD AND ID WAS EXTREMELY WORN AND OVAL SHAPED. THE FRACTURE HAD OCCURRED JUST BELOW THE FLANGE OF THE GUIDE AT THE CYLINDER HEAD BOSS.