I just have waited for others to come in. Tom, you have to find the leak and its there somewhere and the only way to locate it is to begin tearing out walls.
Most leaks are across from the water works and on the floor area.
Most leaks are because of not maintaining grout or silicon caulking the corners properly. Others are due to the shower pan becoming old and tearing.
Your pan might be either a fiberglass bottom, or a concrete flooring with heavy membrane, or just a platform.
But, I would start on the wall opposite from the water works and begin around two feet up from the floor and down ward.
Look for black areas, where water has set, look for mold also.
Good Luck, these things are a real pain and so expensive to fix when they spring a leak.
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