As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A NIGHT TRAINING FLIGHT, THE CREW NOTICED AN ENGINE VIBRATION THAT BECAME VIOLENT OVER A SHORT PERIOD OF TIME. DURING LANDING, THE OIL PRESSURE WENT TO ZERO PSI. THE NR 4 PISTON WAS FOUND DESTROYED. THE PISTON PIN PLUGS (LYC P/N LW-11775) WERE WORN SO SEVERELY THAT ALL OF THEM WERE CONSUMED AND IN THE FILTER. THE AIRCRAFT IN THE FLEET WERE INSPECTED AND ALL THE PLUGS WERE WORN SEVERELY. ALL WERE REPLACED PER LYC SB 12678.