What was found
MIA - INFLIGHT JFK-CUN. CREW REPORTED LEFT HYDRAULIC PRESSURE ON EICAS AND ON OVERHEAD PANEL THEN LEFT ENGINE HYDRAULIC PUMP INDICATED ON EICAS AND OVERHEAD PANEL. APPROXIMATELY 2 HOURS LATER HYDRAULIC SYSTEM PRESSURE LOW ILLUMINATED AND ELECTRIC PUMP PRESSURE LIGHT ILLUMINATED. IMMEDIATELY LOST ALL PRESSURE AND HAD TO USE ALTERNATE FLAP AND ALTERNATE GEAR EXTENSION. EMERGENCY DECLARED DIVERTED MIA LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REPLACED ENGINE DRIVEN PUMP. SYSTEM GROUND CHECK NORMAL OPERATION.