What was found
RETURNED TO MKE DUE TO LOW HYDRAULIC QTY (PRESSURE GOOD), DECLARED EMERGENCY, PERFORMED OVERWEIGHT LANDING AT 140,300 LBS. LANDING WAS SMOOTH AND UNEVENTFUL. REMOVED AND REPLACED LEFT ENGINE DRIVEN HYDRAULIC PUMP PRESSURE LINE FROM PUMP TO PYLON. IDLE RUN AND LEAK CHECK GOOD. HYDRAULIC SYSTEM 'A' QUANTITY AT 100 PERCENT WITH 3000 PSI. REF B737 AMM 29-31.