On/Off leak

Getting the oddest leak from my X-valve/L10/ULT. Whenever I gas it up, there appears to be a leak from the on/off region. Replaced all o-rings (except powertube, powertube spacer/washer, and carried). New reg valve pin and reg piston assemblies. If I press the trigger, the marker fires and the leak stops, but resumes as soon as the trigger is released. Any advice/suggestions?

Toss in a stock on/off from another mag to make sure it's not a barrel leak.

Yes, sometimes a barrel leak can sound like its coming from the on-off area. If it is an on-off leak, it would have to be either the small black ULT oring, or the large white urethane oring around the lower (closest to the outside of the valve) section of the ULT assembly.