As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE ROCKER SHAFT ON THE EXHAUST PORT SIDE OF THE NR 1 CYLINDER FAILED. INSPECTION OF THE OTHER THREE CYLINDERS SHOWED LOOSE BUSHINGS IN THE SAME BOSS ON ALL THREE. THE VALVE SPRING SEAT (PN 24027) WAS ALSO BROKEN, APPARENTLY INCIDENTAL TO THE ROCKER SHAFT BOSS FAILURE. MORE FREQUENT DYE PENETRANT INSPECTION OF THE SUBJECT AREA IS NEEDED.