As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NOTICED BASE NUT AND PART OF STUD MISSING ON TOP REAR STUD LOCATION OF NR 1 CYLINDER. NUT HAD COME OFF OTHER END OF STUD. STUD HAD FAILED AT CYLINDER BASE FLANGE. ENGINE OVERHAULED BY MATTITUCK 1,267 HOURS PREVIOUSLY. UNKNOWN IF STUD WAS NEW THEN. (PART IS COMMONLY CALLED A THRU-BOLT).