www.TheMagSmith.com
This isnt a ULT problem however, when you pull the trigger adn the leak stops, your shutting the on/off off. If the leak persisted, it would be something wrong in the on/off.
I do suggest getting rid of the ULT in favor of a stock on/off, but tune your level 10.
Your carrier is too big, or you have too many shims in the powertube.
Check the powertube and see how many shims are in it. If there are, remove them one at a time and see if that works. If you get to the point where you've removed all the shims but it still leaks, change to a smaller carrier.
Once you find a carrier that will not leak, add one shim at a time to the powertube until it starts leaking, then remove the last shim. You should have a properly tune LX (assuming your o-ring is broken in and I'm not missing anything).