What was found
LOW VACUUM ON THE STANDBY VACUUM PUMP. DURING REPLACEMENT, NOTICED AN OILY SUBSTANCE IN THE INLET HOSE OF THE STANDBY VACUUM PUMP. INTERNAL INSPECTION OF THE PUMP REVEALED WHAT APPEARED TO BE THE SAME SUBSTANCE. THE PUMP DRIVE DID NOT SHEAR, THE VANES OF THE DRY VACUUM PUMP HAD THIS SUBSTANCE ON THEM, CAUSING PUMP TO PRODUCE NOT ENOUGH VACUUM. DURING INSPECTION OF TWO OTHER ACFT , FOUND THE SAME SUBSTANCE IN THE STANDBY VACUUM PUMP INLET HOSE. REPLACED HOSE.