When I run my finger around the underside (rough, unfinished side) of the drain hole, before installing the shoe, it is very irregular and rough (which you can pretty much tell from the photo above, I think). I have only installed a few steel tubs prior to this and never had any issues. I just thought there must be tons of these fiberglass tubs out there, and that maybe there was some special trick that I wasn't aware of (e.g. put a bead of silicone caulk on the underside gasket first?). There are a few fine cracks in the tub finish well away from the drain. I obviously don't want to put in a whole new tub if I don't have to, but it seems this tub might be circling the drain....It is about 26 years old. Thanks for the reply.