vaccume brake chamber on firewall rebuildable?

[hrc200x]

I installed a power brake set up from a later 80s chevy on a '83 cab. This new one has the plastic fluid resivour. The brakes don't work as well as they should. If I push the peddle I can hear air or vaccumme leeking, and also when I push the peddle idle speeds up a 1 or 2 hundred rpm. After engine has ran I pull the vaccume line out of the thing on the firewall and there is no vaccume left there, it does have the one way valve inline. It appears that the thing on the firewall comes apart. Seems a person just has to tap the tabs about a inch counterclock wise and it should come apart. I would just replace, but its already got a nice coat of paint on it. Are these spring loaded or will any parts fly out? Rebuild kits available anywhere or gotta install used parts? Thanks.