Hi Matt,
Tweeter is correct in telling you that your problem with air leaking out of the breath hole in your air tube is caused by the inside edge of the breath hole itself. When a hole is drilled into a tube it can leave a burr on the inside edge that can nick the rear most o-ring on the regulator body, which causes it to leak. I had a similar problem with my Wildcat leaking air out of the breath hole, but much worse...when I got my gun it would not hold air overnight without leaking out. So rather than send it to AOA I ordered the o-rings to reseal it myself. When I took it apart I could see that on the top of the rear o-ring, it looked like something took a tiny half-moon shaped bite out of the top of it! So I took a toothpick and poked it through the breath hole to see if it was clear and lo and behold a tiny half-moon shaped piece of rubber fell out!
When I checked the hole there was no burrs, but I sanded around the inside edge of the hole anyway to make sure it was smooth. And yet every time I put a new o-ring on the rear of the regulator body and inserted it, the breath hole in the air tube it would take a bite out of the rear o-ring. I deduced that the hole had been drilled at an angle instead of perpendicular which resulted in my air tube being like a pickle slicer...no matter how much I tried to sand it smooth it would slice off a piece of the rear o-ring every time, and everytime it did there would be a tiny piece of rubber stuck in the breath hole!
So I eventually replaced the air tube with a brand new one and have never had a problem with it since then. And I want you to know that I have experimented extensively with various regulators in my Wildcat, which means I have had them in and out of my new air tube scores of times and still not one problem with leaks at the breath hole anymore. So you may solve your problem by sanding the inside of the breath hole smooth with 600-800 wet/dry sandpaper, or you may end up replacing your air tube like I had to do.
All the best, Chuck