What was found
DURING CRUISE AT FL400 CREW RECEIVED HYDRAULIC QUANTITY EICAS WARNING FOLLOWED BY LEFT HYDRAULIC SYSTEM LOW PRESSURE INDICATION. FLIGHT CONTINUED TO DESTINATION AND DECLARED AN EMERGENCY. CREW EXECUTED ALTERNATE FLAP AND GEAR EXTENSION. LANDING WAS UNEVENTFUL. MAINTENANCE FOUND LEFT FLAP / SLAT DEPRESSURIZATION MODULE LEAKING AS A RESULT OF A FAILED BLOCK-OUT PLUG PACKING. REPLACED PACKING AND SERVICED LEFT HYDRAULIC SYSTEM. LEAK CHECK GOOD, OPERATION NORMAL.