On the passenger side of the engine bay there are 2 a/c hoses. One of them has a green plastic cap. I noticed that the cap had dirt and oil on it. I think the plastic cap is simply to keep the actual port clean. When I uscrewed the cap I heard a slight hiss, then it stopped. I think I have a small refrigerant leak at this service valve and also lost some of the a/c lube oil mixed in the charge. Anybody else notice this on their car?