Is it the fabric or just the seams that have gone? I have an old but expensive set that leaked badly along the seams. I came across some gel in a camping shop that I painted on and it's done the job. If that's of interest I can dig it out and give you the name.
For Goretex suits. My MPX's are still going strong 6 years and 65,000 miles later.
I treat them once a year with Grangers.
Between times, wash at 30 with a non-bio, then tumble dry in the local laundrette (our home machine isn't quite big enough). Apparently Goretex benefits from tumble drying - it has worked for me and I haven't had any problems yet.
Two stage:
(1) Wash with detergent-free stuff from camping shop.
(2a) Wash in reproofing stuff from camping shop, allow to dry, then use.
(2b) Wash in different reproofing stuff from camping shop (Graingers?) then tumble-dry.
The stuff from (2b) doesn't work if you don't have a tumble-dryer, DAMHIK....