Leaking shower

lg13mza

We've got a small leak under our shower tray and I'm struggling to find the source. It isn't the waste or the supply so it must be getting around the tray somewhere. I've re-siliconed twice around the tray, up the corners of the tiles and door and around the shower taps but it hasn't helped. It is only a very small amount of water, but the tray now creaks as the framework I made underneath to lift the tray has got damp. Trouble is because its in an alcove in an en-suite the only way I will be able to find the route is to rip the whole lot out. Tiles, tray and everything. And then when I replace everything there are no guarantees the problem won't re-appear if I use the same method of install. I'm clutching at straws but has anyone known grout let water through? OR should I have sealed it afterwards with something. We used adhesive for 'wet areas' and Mapei coloured grout that said it was flexible and 'water repellent'. Thankfully I did tank the walls and suspended timber floor before the tray and tiles went in otherwise we would have a much bigger issue than we've currently got. I even siliconed the tray to the tanked walls before tiling so there is effectively two beads of silicone (before and after the tiles). Anyone any suggestions?