As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CYLINDER 4 ROCKER SHAFT BOSS ON EXHAUST SIDE BROKE OFF THE CYLINDER HEAD & WAS BOUNCING AROUND IN THE ROCKER BOX LEAVING A PORTION OF THE ROCKER SHAFT UNSUPPORTED DURING OPERATION. THE POINT OF FAILURE IS UNKNOWN. WHAT IS KNOWN IS THAT THE CYLINDER TOP END FAILED WITHIN 135.6 HOURS IN SERVICE! THE FAILED BOSS WAS FOUND WHILE PERFORMING SB388C AT THE FIRST 100HR INSPECTION POST ACFT OVERHAUL.