Sounds like that small oring seals the air path from the asa/reg to the grip frame of the gun. You may even be able to use the same oring again if it's not damaged. The inner one......obviously replace and lube it up.
ETEK 3LT, with 14" Ti boomstick and cure 3 + bolt F/S
Vanguard creed eyes, membrane, bolt pin, detents, gaskets, schraders, orings and more F/s[/color]
Old school angel poppets/cup seals(LCD and A4/speed), spring detents(not sure which models) F/S