When the shower head is shut off and the water valves (either or both the hot and cold water) are open, we have a bit of water leaking out from the faucet. So... the pressure build up on the downstream side of the valves is causing something to leak. The water is leaking not from the threads but from something within the faucet body.
When the shower head is open, the water stops leaking from between the faucet and the shower wall.
So, I've decided to fix the problem. Unfortunately, I can't figure out how to remove the faucet from the shower wall. This is as far as I've gotten...
I don't want to destroy it while removing it so I'm hoping someone out there can give me a hint on how to remove it.