I had an Avistar and had the problem you are referring to. However, it was not the tank, but the stopper. I have to store my planes in the garage, and during the Winter months on the first season, the stopper shrank just enough for it to leak. I took the tank out of the plane, tightened it up and never had another problem. While I had the tank out, I also cut in a hatch underneath where the tank sits. It did give me a way to open it up and try to diagnose the problem if it came back, but never really needed it.