What was found
LOST HYDRAULIC QUANTITY DOWN TO THE N, RAN HYDRAULIC PRESS/LOSS CHECKLIST. THE QUANTITY STAYED AT THE N. VISUALLY INSPECTED AIRCRAFT, NO LEAKS NOTED. SERVICED HYDRAULIC SYSTEM, RAN NR 2 AND NR 3 ENGINES, CYCLED ALL SYSTEMS, FOUND NR 3 ENGINE HYDRAULIC PUMP PRESSURE LINE UNION LEAKING AT PUMP. REPLACED O-RING AND LEAK CHECKED GOOD IAW DC-8 MM 29-10-1.