That breech should be sealed. My Omega still is... even after a few hundred shots. I'm thinking the plug maker may be at fault here. I'm not sure if T/C outsources this part or not.

Get Jack back on the phone. Tell him it's doing it again with various primers after working spendidly for a short time. Tell him you suspect soft-steel in the porthole at the plug face... thinking it may have expanded. Ask him for a new plug. But this time offer to buy one for a spare. When you get both in the mail, measure both holes but put one plug away for reference later. If it happens again later-on, measure the holes-differences using sewing needles.

I think that's the culprit or the hinge pin needs to be changed because it's creating a small gap - but only from the pressures of firing the weapon. Here's the best one for your model.

http://www.bellmtcs.com/Prod_and_Serv/encorepins.htm

One last thought:

How are you cleaning this plug? Please describe your procedure? What about the break-action shut-seal? Don't describe it... just agree that you're cleaning this area well &cleaning the hinge pin & hole-housingafter every 50 shots for cleaning also. I got this "important" tip from one of poster's Underclocked's posts.