What was found
LOST HYDRAULIC SYSTEM NR 1 QTY IN CRUISE FL370. AMM: 29-11-17-4 JRH: CHAP 6 AMM: 12-12-01-3 CONFIRMED HYD LT EDP & LT ELECT PUMP SWITCHED IS IN OFF POSITION IAW QRH AFTER ACFT BLOCK IN. PERFORMED LEAK CHK FOUND LT DIFFERENTIAL PRESSURE. INDICATOR FOR PRESSURE FILTER AT LT ENG DRIVEN PUMP PRESSURE/CASE DRAIN FILTER MODULE LEAKING. RT & LT DIFF. PRESS. INDICATOR AND PRESSURE FILTER ELEMENT IAW AMM 29-11-17-4. SERVICE HYD FLUID IAW AMM 12-12-01-3. RAN LT ENG AS PER B767 JRH 6. HYD SYS & LEAK CHKD FOUND SATISFACTORY. ACFT OK FOR SERVICE. FOUND DELTA P INDICATOR INSIDE L PYLON BLOWN, DRAINING #1 HYD INDICATOR REPLACED, PRESSURE FILTER REPLACED, SERVICED HYD FLUID, RAN ENGINES SATIS.