What was found
AT CRUISE, THE LT HYD STATUS QTY ILLUMINATED. RF STATUS MESSAGE NEXT TO L HYD QUANTITY. 3000 PSI MAINTAINED UNTIL L HYD PUMPS TURNED OFF. FLIGHT DECLARED AN EMERGENCY AND PERFORMED AIR TURNBACK WITH OVERWEIGHT LANDING. THE FLIGHT LANDED WITHOUT FURTHER INCIDENT. DISCOVERED LOOSE COUPLING CONNECTOR UNION TO PRESSURE LINE ON ELEVATOR AUTOPILOT SERVO, TIGHTENED UNION IAW AMM 22-12-01. PRESSURIZED, NO LEAKS OBSERVED. OK FOR SERVICE. THE AIRCRAFT WAS GROUNDED.