What was found
AIR TURN BACK, DURING CLIMB OUT LOST HYD. QUANTITY NR 1 SYSTEM REF. TO ABNORMAL, ALTERNATE CK. LIST. FOUND LINE FROM OUTBOARD SLAT HYD DRIVE CYLINDER TO CHECK VALVE LEAKING, REMOVED LINE FROM O/B SLAT DRIVE CYLINDER TO CHECK VALVE IAW MM 20-10-01. INSTALLED RT SIDE WING HYD LINE FROM OUTBOARD SLAT HYD DRIVE CYLINDER TO CHECK VALVE IAW MM 20-10-01, NO LEAKS NOTED. OPERATIONAL CK'D NORMAL IAW 27-80-01, PERFORMED OVERWEIGHT LANDING CHECK LEVEL 2 IAW MM 05-51-04, NO ABNORMALITIES WERE FOUND IN THIS CHECK.