Is there anyone who is rebuilding the spring piston, etc. on air rifles that anyone can recommend?
If you want a simple factory grade spring/piston rebuild, I would call someone other than Paul Watts at this time.
Paul Watts is a fine craftsman- no doubt- but he mainly does non standard custom tune blueprinting and rebuilds. Pretty much anything he does for you in a rebuild project will be about $400 includng parts and shipping.
I would contact David Slade. I bet he could do a good factory grade rebuild for about $200 . And NOBODY inthe US (including Paul Watts or Jim Maccari) has wide range of experimnce or factory training on Spring guns that David Slade does. He was Beemans US gunsmith for many years and has factory training from many British and German makers..