As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
OPERATOR HAS EXPERIENCED MULTIPLE VACUUM PUMP FAILURES OF STANDBY PUMP. HE OPERATES PUMP CONTINUOUSLY. AT LAST PUMP REPLACEMENT, FOUND PUMP SEVERELY OVERHEATED. TRACED POSSIBLE CAUSE TO DEFECTIVE PRESSURE MANIFOLD ALLOWING PRESSURE FROM PRIMARY VACUUM PUMP TO BACK UP INTO STANDBY PUMP. AIRBORNE PRODUCT REF MEMO NR 39 REFERS TO THIS VALVE AND RECOMMENDS ANNUAL TESTING AND REPLACEMENT AFTER 10 YEARS. VALVE ON THIS AIRCRAFT WAS 12 YEARS OLD.