How would firearms in cosmoline/crates etc fare up in deep ocean shipwrecks?

[old crow]

A 100% coating of cosmolene would seem impermeable to sea water but the tiniest opening in it would spell doom. I've seen videos of armor being extracted from bogs in Finland and other eastern European areas so the cold non-saline water and the pH must have a lot to do with the preservation of the metal. We see something of the same with the shipwrecks in Lake Superior where the water is salt-free and some 38F year-round; wonderfully preserved wooden and metal shipwrecks.