I seem to be unable to keep fuel from coming out of the wing tank caps on my SS7 whenever the tanks are about 3/4 full or more. I believe the caps are tight and the fuel appears to come out the vent tube. I almost always notice fuel stains on my wings after landings where I used a slip to get down over trees, which I do fairly often. This is becoming a real irritation because the stains are not easily washed off. Anyone have any tips on how to gets the stains off and how to prevent them in the first place. Even when I don't slip it seems to come out with 3/4 tanks. Does everyone fight this on a regular basis?