Welding might not be the best option for worn PVC. I’ve talked to Jacks plastic before, about welding more D-rings to my boat and they do all of the aftermarket work by gluing, not welding. Maybe you can weld old pvc, but I would talk to somebody like Aire about it, first.
The method used at work on the water logged Maravia pads, involves weeks of hanging with the valve pointed down, and a fan, don’t think it gets it all out. (Don't think it’s the pads fault, either, drunk guides doing pack pad races...)
If you decide to operate, it probably makes sense replace the foam, to, like C.B. Said. And add some corner condoms, they are just a circle of pvc, folded, and glued in place, super simple.
The river probably thought, “ he is such an insignificant, pitiful, little creature, with such a short time to live, I will let him go this time, and try to teach him something” - Buzz Holmstrum