As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE REMOVING THE TRIM TAB ACTUATOR FOR SERVICE, BOTH GROOVE-PINS (P/N 3/32X.38TYPE3) WHICH ATTACH THE ROLL CHAIN SPROCKET, (P/N 0310332-0) TO THE SCREW-INTERNAL THREADS (P/N 1260049-1) OF THE TRIM TAB ACTUATOR WERE FOUND TO HAVE SHEARED. THIS ALLOWED THE SPROCKET TO BE SLIPPED OFF BY HAND. ONLY FRICTION BETWEEN THE SPROCKET AND THE SCREW-INTERNAL THREADS WAS ENABLING THE TRIM TAB TO BE MOVED.