You had flawed nickel plating and you put it in vinegar? The vinegar will eat at the exposed copper and cause even more flaking. I'd do the same as wermad and blast the blocks clean and them polish the underlying copper...
The block was still pretty gunked up so I put it in a diluted bath with one part vinegar and 20 parts distilled water and it didn't really have an effect on the already exposed areas. Not much different from ketchup which has vinegar and even citric acids from the tomatoes. It did happen to create new exposed areas which might of resulted from microscopic fissures in the platting. I probably would of expected the same thing to happen in just plain distilled since that was where the problem first occurred.
I'll check how much it would cost to re-plate them. Either way I'll have to blast them.