What was found
BOS - FLT 674 - DURING DESCENT A HYDRAULIC SYSTEM 1 LOW QUANTITY MESSAGE APPEARED. THE FLIGHT CREW DECLARED AN EMERGENCY AND DIVERTED TO BOS WHERE THE AIRCRAFT LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE NOTED THAT THE SYSTEM 1 HYDRAULICS QUANTITY WAS AT 44 PERCENT. REPLACED AN O-RING ON THE LEFT ENGINE SYSTEM 1 HYDRAULIC PUMP SUPPLY LINE. LEAK CHECK AND SYSTEM TEST WAS GOOD. AIRCRAFT WAS RETURNED TO SERVICE (M)