Sealing the tub and surround to fix leak

robsouth wrote:
... The floor pan goes up the outside of the shower walls a substantial amount ... at least 6" or so. ....

Maybe on some units but NOT on mine. My plastic tub and seat are one piece. At the top of the tub there is a plastic surround and a small gap between it and the tub. There is NO overlap. The manufacturer had put a small amount of sealer but there were voids. In that case silicone tub caulk IS the correct thing to use.