This is my way how I eliminated or minimized couple of issues some people still noticing or experiencing today. What I did was a progress through past 2-3 years and not a single afternoon brainstorming, may help some people next time doing a surgery on Impact variants.
Lets start with barrel/liners. I am running with floating liners on orings, tried several other scenarios and I am back to square one.
I replaced the orings inside barrel to NBR 90.
The Liner Lock (#10) have a single oring for .25 and two orings for .177 and .22;
The Barrel Inlet attachment (#5) has also a oring as well. These orings doesn't seal but locating/floating the liner.
Easy to assume that frequent removing the liner for cleaning will sooner or later wear out these orings, especially if there are some sharp edges on liner ends.
I would assume you never squared up your liners?
How about putting a radius on the outer edges breach side to minimize shaving off the rubber when reinstalling the liner? Also silicon lube it well when reinstalling.
I made a tool with abrasive diamond powder creates a small conical pocket into the Liner Lock, also cut a small chamfer on the liner muzzle edge, with a diamond paste I lapped these together.
This will lock the liner in same place no matter how many times removed.
Lapping the lead-in is as important as the re-crowning.
Installing the liner back into barrel and need a consistent torque for the Nut.
The next question is - how easy is the barrel sliding back into its place?
Any parts misalignment issues?
And that is a next long story how to assemble and torque properly.
If that would be me, I would take all apart, and once in pieces
I would (I did ) replace the PUR oring inside Plenum to NBR 90;
Polish to mirror finish the Valve Rod the portion that slides on the NBR oring, also refresh the 2 MM oring;
Polish the Valve Seat
Polish the Reg washers
Polish the Reg piston
Polish the Hammer and Valve spring ends
Check for wear on Hammer insert
Chose the right transfer port
Kind of loosing my gravity at the moment. Most likely I forgot to mentioned some important things, Please feel free to chime in