Thought about this some more. I have several firearms that are 80+ years old (I'm thinking of my Russian Mosins, the Mausers, etc.) or even 50+ years old (the SKSs, Garands, etc.). These are weapons that were carried, trained with, used heavily in dirty, wet, muddy, harsh conditions; yet they are steel and wood and still funtion just fine and, aside from evidence of use, they are in good shape. Heck, the bolts on some of my C&R rifles look like they were machined yesterday!
I venture to guess that my weapons will never see the abuse these ones saw, and my modern ones are made of tougher materials than those. And they are pampered in comparison.
If the war implements are still fine after a 5, 6, 8, 10 decades, then lasting 10 times that, being rarely fired and cleaned after each use, stored in my climate controlled house will have zero effect on them.