Prior to disassembly, try the tissue paper test over the breach to check for proper breach seal.Get a maccari seal for the Talon,and and adapter for the seal(ask for one on the boards), use the same spring if new,just grind(stone)smooth the ends and deburr the tube after degreasing it first. If spring is damaged or not new AA Skiff sells replacements.He posts on this board as well.
Check lockup and mating of the breach and block,barrel tightness and eccentricity coming out of the block. Lightly smooth the transfer port if it is at all snickered up or out of round, if not just clean well with alchohol and q-tips or a pipe cleaner.
The 1250 breach extend outwards from the block, most other airrifle are flush/recessed breach sealed.The hunter extreme may or may not be alike, I don't have one so I only ASSume.
Then debur/polish the piston and the add the adapter and new piston seal.Relube per CDT tutorial(I like to go light on anything going internal including tar). Season to flavor and shoot!
Get all materials and parts first-then start home tune-learned this the hardway.
Hank