I have this problem with both the stock valve and my Boss valve but I don't have any problems or leaks. I have over 2000 shots on my Boss valve with the original o-ring and I still have no problems and that's with 1600psi of pressure in it. I don't use any kind of thread lock or tape either. I think tape would work to help tighten it up, you might also see if you can find a bigger (fatter/thikcker) o-ring and see if that helps too. I'm not sure if they designed the valves that way to allow everything to line up perfectly but I bet it's because they make the end caps seperate rather than drilling the intake hole while it's threaded on the valve body. I have 2 stock valves and a Boss valve for the AS2250 and they all do it. Once the valve is pressurized the end cap is almost locked in place.