I just discovered that one of my tub valves was leaking inside the wall for quite some time, given that the wood floor in the adjacent closet has gone moldy and the drywall beside the tub out past all the tile is soft. It was probably 1 drop every second.
Last night I installed a couple ball valves so I didn't have to leave the whole house turned off while I mess around with this, but I am not 100% what to do next. The leak is coming from some sort of adjustment valve right under the cold water handle. I don't know what this thing does or what it is called so I am having trouble searching for a solution. It is accessible from the tub side through a hole in the valve trim plate, right underneath the handle. See the hole in the photo below. Anybody know what this is and how to repair it before I just start taking it all apart?
The drywall behind the thickset mortar bed tile was totally disintegrated in this area. There was insulation wicking the water all over the place. Without the insulation the leak probably would have just gone down the hole in the slab for the drain. For reference, the house was built in 1977, slab on grade in north Florida.
I pulled the handle off to get a better look. The bottom adjustment piece is where it is leaking from. What does this thing do? I'll need to get a special wrench to open it I guess. My sockets don't fit with the tile there.