As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING INSPECTION/TROUBLESHOOTING OF ENGINE FOR ROUGH OPERATION/BACKFIRING, FOUND EXHAUST ROCKER LOBE OF THE #9 CYLINDER CRACKED THRU EXHAUST PORT AND AROUND EXHAUST VALVE SEAT. TOTAL TIME OF CYLINDER IS UNKNOWN. ENGINE IS 1157 HOURS SINCE MAJOR OVERHAUL. CYLINDER HAD APPROXIMATELY 300 HOURS SINCE OVERHAUL.