I used Gear Aid ReviveX for my klim bibs that started to let water through the seat. It worked well for me. I don't have a good long term update for you though. After I used it, I rode probably 6 more times before I sold my sled. That being said, it's still holding up when on the sledding hill with the kids.
In the past I used the Nikwax products for my North Face GoreTex ski jacket. It never really did the job as well as I thought it should. It would let water through after just half a day.
I would almost second the idea of using thompsons waterseal, except that both nikwax and revivex are marketed to still allow the goretex fabric (or whatever brand you have) to continue to breathe. The thompson waterseal product will seal it up completely. I sweat quite a bit, so that was not worth it for me. If you're not worried about breathability, I think this would probably be the absolute best method to keep the water out.