The shower was installed in new construction abourt 35 years ago. I've had two plumbers out. It is not a pipe and not believed to be the drain. Filled the pan. No leak. Ran water down the drain. No leak Ran the water over the tile and it bagan to leak so it seemed to be a grout problem, so I regrouted and it stopped.Recently, the other tiles needed to be regrouted, so while it is curing, three of us are using the shower over the foyer and it began to leak again. The ceiling has been repaired several times from the damage and from plumbers and contractors trying to find the problem. I'm at a lss, as are the pumbers and contractors. Any other ideas besides tear out the shower apart? Thank you.