If it doesn't work with all barrels...
The your problem in inside the frame (hammer, sear, etc.) and it needs a smith that knows what he is doing.
I have heard of problems with some barrels and frames, but never see one myself. Usually I hear of barrels that won't unlock. Youir problem sounds like something worn/broken (or possibly just fouled too dirty -you can hope) in the lockwork. T/Cs are not terribly complicated guns, but they are not a beginning tinkerer's project either. I recommend professional help. You might even call the factory, your G2 can't be that old,, might it still be under warrenty?