If rusting was a problem when iron balls were stacked on an iron "monkey", I'd have thought the electrolytic action when iron balls were stacked on a brass monkey (particularly in a wet/salty environment) would be even worse.

And, anyway, wouldn't rust have fused the balls together, as well as to the monkey?

Guest Knappo's original post sounds like a myth to me.

Incidentally, this is my last post as "Bald Eagle": my nom de plume causes too many folks to assume I'm American (I'm English). From now on, I shall appear as "Ringer".