As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON REMOVING THE ENGINE TO MAIN GEARBOX SHAFT TO REPLACE THE MAIN GEARBOX INPUT SEAL. I FOUND THAT THE CASTLATED NUT THAT HOLDS THE ROTOR BRAKE DISK IN PLACE WAS LOOSE. REMOVED NUT, WASHER (SIGNS OF SPINNING IN PLACE) BRAKE DISK, LARGE FLAT WASHER UNDER DISK AND FOUND THAT THE LARGE FLAT WASHER HAS WORN A GROOVE INTO THE GEARBOX FLANGE. REMOVED FRICTION RING AND FOUND THAT IT WAS STEPPED AND THAT THE INNER BASE THAT GOES TOWARD THE GEARBOX HAD SIGNED OF WEAR.