I've rebuilt several fuel pumps for my car, a 64 coupe. When I'm done I vacuum test them by plugging the input and pulling a vacuum on the output using a MityVac, 25 inches Hg. I've found seal issues like this but have never had one hold a perfect vacuum. I can get it down to a very slow loss rate but they eventually draw air somewhere at a very slow rate. Will a tiny air leak become a gas leak in use? Does anyone have any experience here? I'm going to test my MityVac tomorrow to see if it is the issue but I don't think it is. Is it possible that I'm getting an adequat seal?