Its a common misconception and also a marketing dream that goretex can be re treated!
I went on a goretex course a few years ago when I worked at a BMW dealership.
Goretex is from scotland, it was discovered by mistake and is a closely guarded secret in how its made, it has many patents, which is why there are so many other 'copies'.
Basically goretex is a membrane which after its production process is full of holes, These holes are, smaller than a water droplet molecule but bigger than a water vapour particle, hence waterproof and breathable. Goretex works better if there is a temp difference, thats why it always works well for walkers and other kind of sports as you generate a lot of heat. They also say it works better when wet to get rid of moisture on the inside!
However not always good for a biker as there isnt as much heat difference each side of the goretex so it doesnt really know which way to pass moisture vapour if you like.
Hence going on this theory, no re-treaters are ever going to work as goretex is not a treatment waterproofer like say a silicone coating, it just is a culinder basically.
Goretex only leaks when eother the seams split, it has a hole in it or it can actually wear out, ie go thin.
If you wash goretex and use softener it will make it leak as the softener makes the goretex wick moisture in.