-- Last Updated: Nov-16-12 9:04 PM EST --
Every post I saw which spoke directly in answer to your question said that neoprene is waterproof. However, a few people pointed out that the seams can leak, one person said that if you walk on the fabric for a long enough time (as is the case with the stocking feet of neoprene waders) it will wear out and leak, and Dr. Disco said that a really long time ago the stuff was not as good, but that what's available now is certainly waterproof, so since your boots don't date back "to the dark ages" ("several years old" is pretty darned new, as neoprene production goes), this would not apply (but I'm skeptical and think that his example is just another case of leaky seams, since neoprene is basically just synthetic "rubber" which by itself is totally impervious to water). So, simply in regard to the whether the fabric is waterproof, that's a unanimous "yes" by my way of thinking. Just find the leaky seam and fix it.
Oh, and since waders came up in discussion, would anyone think that they'd be made from a fabric that is NOT waterproof?