Trojan finish problem

[Phil Yearout]

I've owned this Trojan for quite a few years; I always assumed the wood had been refinished but I never thought about what the finish might be. On a recent trip I hunted in the rain and now the stock finish is very splotchy - almost looks like bare wood in places. Forearm is fine. I've never had anything like this happen before and it seems very weird to me. I don't know if you can tell from the photos but it really looks pretty bad. Any ideas as to what might have happened, what the finish is, what I ought to do about it, etc.? Thanks...