Dave- after stripping 2 cheeseball 3/8 drive torque bits, I found that grinding one down to get a better bite did the trick. This was the first time my T-stat was touched in 205k miles and I did not think to spray them in advance. Once I put liquid wrench on them and jiggered around with the one remaining torx bit I had, it finally loosened up. The bits I had were from some crapola Wall mart type torx kit...5 bucks for a zillion bits type of thing. You get what you pay for! Though I guess I'd rather strip the bit than the bolt head.

Good luck.