As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) CYLINDER NR 4 REMOVED DURING 100 HR INSPECTION DUE TO OIL CONTAMINATED SPARK PLUG. TOP COMPRESSION RING FOUND IN SEVERAL PIECES EMBEDDED INTO PISTON. ALL CYLINDERS REMOVED FROM BOTH ENGINES, 8 TOTAL AND 3 OTHER PISTONS FOUND WITH CRACKED TOP COMPRESSION RINGS. NOTE THAT ALL OTHER CHECKS WHERE NORMAL, COMPRESSION TEST RESULTS ABOVE 70PSI. AFFECTED CYLINDERS SENT TO OVERHAUL FACILITY FOR REPAIR/REPLACEMENT.