TiPX Leak Help

Hopefully someone can shed some light on a very tiny leak emanating from what sounds like the air valve of my recently purchased second-hand TiPX pistol. In a preliminary tear-down, I've checked the gas line o-rings (both long and short, nothing broken, nice and greasy), the firing valve was nice and flush (tightened down), greasy, with o-rings intact, and the leak happens with either the regulator plug or the remote line installed.

When I go to release gas manually through the pressure relief valve the leak sound it makes it separate from the one I hear internally so I'm assuming that isn't it either. When I take a shot and keep my finger held on the trigger the leak goes away, but comes right back when the marker re-pressurizes for another shot. I've taken apart and put back together the regulator and there is no debris and all the o-rings are intact.

Any other things I should be trying? I feel like I'm wasting so many CO2 cartridges just trying to fix this problem. Hopefully someone has seen something similar on their workbench. Thanks for taking the time to read through my issue, I look forward to your inputs.