There are 2 check valves on your car. 1 at the hood between the nozzles. The other is incorporated into a white plastic tee near the pump. The tee conects to the pump, the hose running up to the hood, and the third line is a vent hose about 8 inches long that hangs in the air. There is a small metal ball thats supposed to close the vent when thhe pump is activated and direct full pressure to the hood. The ball is not closing the vent, hence your leak near the reservior. try cleaning the tee, or replace it, or simply plug the vent hose with a golf tee. Won't hurt a thing.