When I used to hunt ducks a lot, I used to take the stock off my 870 and/or 1100 quite regularly, and there was often moisture in there, and sometimes light rust. I'd grease the bolt up pretty good and I'm sure that helped. I didn't tear it down like this after every hunt, but on the days when I was in a heavy rain all day, or especially those times when the gun went swimming I would.
Hopefully Remington will get it all fixed up for you.