Replaced stem and seat of bathtub faucet. It still leaks. Valve body?

[jtm]

I did the job in August and it was cured. It's back again. Replaced the washer. The seat looks good and smooth. It was threaded into the valve body properly. It is snug, and there is no movement I do not think I damaged valve body but do not know what to look for. In the wall, it looks fine. What are signs that the valve body has been damaged? Could inadequate pipe dope on the stem cause the leak? Any other chronic leak tips?