to add onto your list of o rings as a part of the air pressure, you have one under that tiny pan head screw on the right side behind the vent hole(it’s the one screw some people never swap out when doing a stainless fastener conversion), the bottle itself has 3 o rings, and this next area ive never verified, but it’s the two plugs at the front and one at the rear of the trigger block. The front is hidden by the bottles Dowty seal, and at the rear it’s hidden by the hand grip. It’s the tunnel that FX drills thru, that is the pathway of air pressure to the regulator. Not looking at the parts diagram at the moment, but I could’ve sworn there were o rings under those screws.There's quite a few orings on the impact yes but far from all are under pressure all the time to cause this.
Gauge xrings
Small oring at the end of valve pin
Orings on valve house
Two outer orings on small end of plenum
Inner oring on plenum that seals against the valve rod.
Regulator orings
Off the top of my head, I'd get some leak detector and check these areas.