maybe the valve or the bullnose part has a scratch on it. really you want zero leakage, but if its only leaking say a few psi an hour, its not that much that you will even notice it. your only going to have the valve open when welding then shut it off. over the life of the cylinder, you may lose 20psi once your all said and done. really you wont know if it was the valve or your regulator until you test it on a new cylinder.