I'm sure the shells are fine. I'm shooting stuff 30 years old no problem.
The oil probably is gummy too down there helping it stick. Hose it down with an electrical cleaner or gun cleaner that doesn't leave a residue streak.
I tried a powder lube down there based on recommendations I'd read but switched back to a light oil down there with bi-annual degreasing.
You still might have to pop a pin to look at that spring, but sounds like a typical old gummy oil gunk prob to me. That's usually what my old Winchester single shot used to do...ain't she ugly? Bought her in 1979 and me and my buddy chopped'em down for them darn fast flying partridge.
Every man should have a sawed off shotgun...make sure she's legal per ATF though with a 18" barrel and 26" overall or you gonna be in trouble.