We have a fiberglas shower stall in our basement. The stall is two piece and framed and drywalled on the exterior. Recently we noticed water pooling on the bathroom floor. After some investigation revealed common causes not to blame, I called a plumber. He advises that ground movement has caused the shower strainer to separate from the drain line. He said the strainer, which he called a big nut, goes on before the shower pan and the only way to fix this is to remove the shower stall and replace the strainer and reinstall everything. I am a tad skeptical as he indicated he had never seen anything like this in his 37 years of plumbing. Anyone have any other ideas? Thanks in advance.