As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DIRECTIONAL GYRO FAILED DURING REPAIR. INSPECTED ALL VACUUM FILTERS FOR CONDTION. B3-54 FILTER BROWN IN COLOR AND 1J10-1 FILTER WAS ORIGINAL FILTER FROM DAY OF MANUFACTURE OF AIRCRAFT. DATE CODE FOUND ON FILTER 2Q74. REPLACED BOTH FILTERS. SUBMITTER STATED MOST LIKELY CAUSE OF DG FAILURE IS CLOGGED FILTER. NEED AD OR MSB TO INSPECT AND CHANGE OLD FILTERS.