Atsko makes a product called Welt Seal that has worked for me in the past. You may be able to find it in stores depending on your area. My WalMart starts carrying Atsko products around hunting season. http://www.atsko.com/products/waterproofing/welt-seal.html
waders are meant to have a much shorter life, regardless. I've had cheap ones and fairly expensive ones. Leaking is the end result of all waders.
I've used shoe goo, which is perhaps too thick. I extended the life of my present waders by spraying the seams with silicone spray. Preventive care!
Now I'm getting a little "dry rot" with some small cracks on a fold seam. I guess hanging waders, when not in use, lengthens longevity. Maybe the next time. I now have some room to hang them.