What was found
C SYSTEM QUANTITY GAUGE INDICATED ONE-QUARTER AFTER GEAR AND FLAPS WERE RETRACTED. PRESSURE STAYED NORMAL 3000 PSI LOW QTY LIGHT STAYED OFF. PRODCEDURE ACCOMPLISHED, SYSTEM SHUT DOWN. WHEN GEAR WAS EXTENDED LOW QTY CAME ON. SYSTEM WORKED NORMALLY. (ATM WAS USED TO LOWER GEAR). FOUND O RING BAD ON PLUG FITTING ON BACK SIDE OF LANDING GEAR MODULE IN HYD SERV CENTER. REPLACED PLUG AND O RING AND PRESSURIZED HYD SYSTEMS. LEAK CKS GOOD.