If you wipe rubbing alcohol on the outside of a goretex garment then turn it inside out - there will be a gray circle on the inside - the center of that circle is the leak. I learned this fixing the same pair of Simms waders for the last 8 years. Bushwhacking with waders on will lead to pinholes and just general abusive use will also cause leaks. Once I find the leak I use goop marine or plumbers sealant on it. And the leak is fixed. I have never tested this on any other breathable fabric. Just thought I would throw that out there.
Credits: This was taught to me by the Simms rep at my local fly shop.