What was found
BWI/CMH - FLT 2401 - AIR TURNBACK. A-SYSTEM HYDRAULIC PRESSURE LOSS. CONTRACT MAINTENANCE VERIFIED INDICATION ONLY, BUT HAVE HYDRAULIC TRANSFER FROM B-SYSTEM TO A-SYSTEM. WHILE TROUBLESHOOTING, NOTED HYDRAULIC FLUID FLOWING FROM RESERVOIR OVERFILL TUBE WHEN STANDBY PUMP RUNNING. A-SYSTEM UNPRESSURIZED. NOTE: B-SYSTEM RESERVOIR DOWN BELOW REFILL MARK. REMOVED AND REPLACED NR 1 ENGINE THRUST REVERSER SHUTTLE VALVE PER MM 78-34-11. LEAK CHECK GOOD. PLACED ON MEL 29-03. REMOVED AND REPLACED TRANSMITTER FOR A-HYDRAULIC SWITCH. OPS CHECK AND LEAK CHECK GOOD. MEL CLEARED. (X)