Shower Stall repair...

Loulou57 is correct, at least in part. First you have to stop the crack from generating any more. You do that by drilling a hole, probably 1/8" is enough, 3/16" better, at each end. The sharp end of the crack is an infinite stress riser, the round hole reduces it tremendously. As far as sealing the crack the believers in the 3M products are probably right. Personally I'd use some of my boat building epoxy as that's what I'm familiar with and have. But first you have to stop the crack from getting any longer.

I would assume it's some sort of plastic. It is pretty flexible so I don't think it's fiberglass.
I think I can do a fairly clean job if I were to use fiberglass. I know it wouldn't look as good as replacing the complete stall but it would be better than having a wet wall behind it.

If I were to use a fiberglass resin on it and it is indeed plastic then I would be afraid it would eat the plastic.

I hate to use a silicone or sealant. But it would be better than ruining the wall behind it.

Ours is fiberglass so fiberglass repair can do just fine but assuming you don't know how to do it yourself, it's probably cheaper to just put in a new one rather than pay a guy to do a good color matched job. If you don't care about the appearance on the other hand, it's a pretty easy job.

Silcone is a horrible idea. I guarantee before the first weekends use is out, it will be leaking.

What material is yours made of?

do not use silicone. use 3M sealant 4200/5200 et al.
bumpy

We are getting our 2011 TT shower repaired under warranty. We never used it so didn't notice it until we went to on our last trip out. The service tech said for a small crack they drill a very tiny hole at each end of the crack. Then they insert a sealant with a syringe. They push down and when dry you never notice it. Ours has had a crack for a while, since new they figure, beside one of those little button like covers. They are completely replacing the tub surround.

So what material is yours if not fiberglass?