The shower stall is 30+ year-old square inch tiles. At the base of the wall on the very bottom row of tiles above the shower floor there are 4 tile pieces that are pushed in to the wall which are causing water to leak behind the wall into a closet, and then downstairs to the neighbors apartment. How can I know for sure if the pan is leaking? And how can this problem be repaired? I'd like to do some minor remodeling in the whole apartment, but never thought I'd have to ripe apart the shower/bath tile walls. How many contractors would have to be hired for the job if I just wanted to install a one-piece fiberglass shower? HELP!!!