What was found
LT HYD QTY DECREASED DURING FLT. PRESSURE ONLY DECREASED AFTER ENGINES WERE REDUCED FOR DESCENT & THEN PTU BECAME INOPERATIVE. BECAUSE LT QTY IN 0, RT ENG PUMP OVERHEAT LIGHT ON ALSO. FLT RETURNED TO BOGOTA. INSPECTION WAS FOUND MLG DOWNLOCK HOSE RUPTURED. THIS AIRCRAFT HAS ACCOMPLISHED THE SB 757-29-0056, AND REMOVED HOSE HAS PN: 271N6119-2. PTU CONTROL PRESSURE SWITCH WAS FOUND WITH FAULT. MAIN LANDING GEAR DOWNLOCK HOSES WERE REPLACED, PTU FILTER MODULE WAS INSPECTED AND WAS FOUND IN NORMAL CONDITION. PTU AND HYD PRESSURE SWITCHES WERE REPLACED AND TESTED IAW AMM. EDP (LT) WAS REPLACED IAW AMM. "HIGH ENERGY STOP/HEAT DAMAGE CONDITION INSPECTION" WAS PERFORMED IAW AMM WITH NORMAL CONDITION.