What was found
DFW - FLT T0455 - DURING CRUISE, NR 1 HYDRAULIC LOW LIGHT ILLUMINATED ON MFDU. CREW TURNED OFF NR 1 HYDRAULIC SYSTEM AND FOLLOWED PROCEDURES FOR ALTERNATE FLAP AND GEAR EXTENSION. AIRCRAFT LANDED DFW WITHOUT FURTHER INCIDENT AND WAS TOWED TO THE GATE. MAINTENANCE FOUND O-RING IN SAMPLING VALVE LEAKING. REPLACED O-RING IN SAMPLING VALVE AND SERVICED NR 1 HYDRAULIC SYSTEM. SYSTEM GROUND AND LEAKED CHECKED, NORMAL OPERATION. (X)