I'm passing this along in hopes it may save others from having to go through the PIA repair work I just spent about 10 spare time hours doing this week.
The design of these valves hasn't changed much in the past 20 years, and when the diverter valve seal gets leaky, the water which leaks past it while filling the tub or using the shower ends up BEHIND the wall the valve is on. The diverter valve is the one which switches the water flow from tub to the shower. There's an O-ring seal in it which doesn't last forever.
That seal in one of the Temptrols in our home hardened up and started leaking, and I wasn't aware of it until water started dripping through our kitchen ceiling and into my corn flakes while our daughter was taking one of her interminable morning showers upstairs.
In addition to the kitchen ceiling, the dribble had been soaking and wicking through the plasterboard behind the shower wall tiles. I had to take off about 30 tiles, replacing the soaked plasterboard with carefully pieced in cement board and stick the tiles up again. (All the while cursing the "quality builder" who'd cheated us by not using a proper waterproof backer board when he built the place.)
So, those of you with Temptrol tub/shower valves would be well advised to check that O-ring seal in the diverter valve and replace it once in a while. Ours are about 18 years old now, but I've no idea for how many years there may have been a slight drip coming from last weekend's culprit.
I added a "fix" on all the Temptrols in our house by using silicone bathtub caulk to glue a little U-shaped sheet brass "drip chute" to the bottom of the diverter valve housing, angling it so that any future leaks will end up on the "user side" of the tile wall, behind the bottom of the trim plate. From there, they'll harmlessly run down the tiles and into the bathtub.
Happy Holidays,
Jeff
-- Jeff Wisnia (W1BSV + Brass Rat '57 EE)
"If you can keep smiling when things go wrong, you've thought of someone to place the blame on."