I had the same issue with an old pair of waders long since retired.
I fixed them with aqya seal. Found the pin hole by sitting in the bath tub with cold water and just skibbiis on, when I felt the cold water, I got up yanked em down and saw the approx location of the leak. Blow dried the inner part, then circled it with a sharpie, next I walked to the ditch down the street and (after putting on some shorts of course) waded into the ditch for about 1 min then got out and found the pin hole.
Sealed

er up and never leaked again.