It's the block itself. I believe it can be stopped. I think it the block were to be decked to clean it up good. Have it decked so it has a little "tooth" to it. Not a mirror finish. Then degrease it with denatured alcohol, let it dry completely and come back over it with a high temp oil based DTM paint. Just spitballin, but that would certainly stop the corrosion problem. Now, what it would do in terms of affecting the gasket sealing, I don't know, but I'd be game to find out.
