I used Easy-Off BAM! & a Clorox stiff brush from Target and it worked like a miracle. The Easy-Off said not to use on metal but I figured that by the time the metal was reached, I'd already have most of the build-up off. I am SO HAPPY! Thank you, barnmom, for the ideas.

First thing I'd do is flood the pan. If you think it's the pan itself that's leaking, then I'd plug the drain and flood the pan with water, to just below the height of the curb. If it stays dry your pan is fine and it's time to look at the walls and what's behind the walls. Is water spray that ricochets off the bathers' body getting behind the valve trim and into the walls? It almost sounds like water is getting behind your tile, and it was trying to get back in where the wall meets the floor. The water saturated your caulk, which if it's a latex caulk, will stay mushy if continually exposed to water. When he sealed this joint tight, the water had no where to escape so the water eventually backed up high enough to get into your framing bays and drip down to your kitchen ceiling. Is this the same one where we thought you might have a plumbing leak inside your wall? Did you have the saturated and swelling shower curb? If this was an acrylic base, then I'd say yes, the weight of your son could cause a leak that might not occur were a bather not standing in the shower. But with this being a solid tiled floor...I'd say no. Depending on the age of the valves, it could be what Bill wrote. The packing or stem of the valve has come loose a little bit and it's dripping. Example, if the hot water side is leaking and your tiler only ran water from the cold water side, then it never would have leaked. That's a stretch, but worth looking at. Can you pull the valve trim kit so you can see the valve body and run the water? Sometimes you can wad paper towels up, wrap them around the pipes or tuck them under the valve body where you can't see or touch, and see if they become wet. I've also seen leaks happen depending on what spray was used on a multi-spray shower, some sprays cause a little more back pressure in the plumbing, that can cause a leak at the arm, or at a sketchy soldered fitting. One last thing, the door. Does the door, it's hardware, or trim, funnel water in any way shape or form across or down the wall? Many possibilities, all frustrating to say the least. Mongo

Update - We finally had the repair done. When the tiles were pulled off, the tile guy found a broken piece of wood about 6" long. I recall that the original installer had used full length boards as temporary overnight supports. We speculated that when he removed the board, part of it broke off and he either wasn't aware or didn't bother to retrieve it. In any event, the wood was quite wet and had obviously been leaching through the tile for some time. Problem solved! Thanks so much for all the input. Nobody got the right answer, unfortunately, but at least we got it figured out.

We don't have the tub tracks any longer, but they are sort of like regular window tracks, which drive me crazy with the dirtiness. With window tracks, I've gotten in the habit of every so often, flooding them with cleaning solution (largely water), scrubbing them with an old toothbrush, and then sucking the water out with a wet/dry vac with crevice tool attachment. Sometimes you have to add more water, as a rinse, and vac it out again. It's so hard to get rid of the gunk in the corners otherwise. If you have access to a wet/dry vac, I recommend trying that.