What was found
L HYD QTY DECREASE TO 0.06 WITH EDP PRESSURIZED AND ACMP OFF; HYD QTY CONTINUED DECREASING. AIRCRAFT RETURNED TO BOGOTA.CORRECTIVE ACTION:LH DIFFERENTIAL PRESSURE INDICATOR WAS FOUND WITH LEAK. DIFFERENTIAL PRESSURE INDICATOR WAS REMOVED AND BOTH PACKINGS WERE REPLACED IAW AMM 29-11-15 PAGE 401 AND AMM 20-10-19 PAGE 401. LH HYD SYSTEM WAS REFILLED IAW AMM:12-12-01PAGE 301. ENG RUN UP LEAK CHECK WAS PERFORMED WITHOUT DUPLICATING FAULT.