As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A ROUTINE COMPRESSION CHECK, AIR WAS FOUND LEAKING THROUGH A POROUS CASTING IN THE CYLINDER HEADS ON THE NR 2 AND NR 6 CYLINDERS. BOTH CYLINDERS WERE REPLACED. SUBMITTER SUGGESTED POSSIBLE CAUSE AS DEFECTIVE CYINDER HEADS INSTALLED ON CYLINDERS AT MANUFACTURE OF THE ENGINE.