Hmmm!
In a regular Spray rig that would be indicative of a leaking seal or "O" ring. I don't know about yours, so i am not going to comment on that. My stuff is mostly old DeVilbiss and Badger stuff that has been rebuilt so many times i don't think there's a stock part left in e'm!
The one thing I always wondered, does that Hobbyist level Airbrush have the shell quality to prevent Internal wear on the surface of these parts? Prevent, in the sense that they have a hardened surface or something like that where these parts slide or rub together!