As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A HOLE WAS FOUND IN THE VALVE COVER. THE SHAFT OF THE VALVE ROCKER ROTATED AND WORE THROUGH THE SIDE OF THE VALVE COVER. SUBMITTER STATED HAVE SEEN SIGNS OF THIS KIND OF WEAR, BUT NOT TO THIS DEGREE,3 OF THE REMAINING 6 CYLS SHOWED SOME SIGNS AND WERE REPLACED. A NYLON PLUG IN ENDS OF (21153) SHAFT-VALVE ROCKER WOULD STOP THIS ACTION.