Someone else will have to verify this. But, I believe you might already have the most recently updated B2 Piston. If it does turn out you have the most recently updated piston it used to be you could purchase the outer Teflon seal separately.
That only leaves the Seal and the Bushing. The Bushing is also likely the updated white nylon one but it is inexpensive if you want to replace it.
And of course the cover O-ring.
Repair Links
Fast navigation
http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html