What was found
DURING CRUISE, CREW NOTED GREEN HYDRAULIC SYSTEM QUANTITY DECREASING AND RECEIVED HYD G RSVR LO LVL MESSAGE. CREW FOLLOWED COCKPIT OPERATING MANUAL PROCEDURE, DECLARED EMERGENCY, DIVERTED TO DTW AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED LEAKING O-RING SEAL ON POWER CONTROL UNIT VALVE BLOCK FILTER (24CV) AND RESERVICED HYDRAULIC SYSTEM. LEAK CHECK OK.