I've noticed a water stain in my living room ceiling directly under where my shower is. I did some measuring and I believe its coming from behind my shower wall, but since I'm not a plumber, just speculating at this point. Any help?

You must localize the leak. Cut a square hole in the ceiling , (save the cut out piece you'll use it as a patch later). Check around the trap for moisture, Check the wall line to see if the water's coming from the wall. Let me know what you find. Tom