I bought a 400 off an individual and it hadn't been shot in a couple years and when the seller was boxing it up he noticed it was empty. I've had more than a few airguns apart but was just wondering, while waiting for it to arrive, what are the likely leak points and do these rifles have any common leaks? From the drawing I looked at there are only a few orings that would cause this. The reg, the fill valve/ bottle adapter and the firing valve.