I just took off my intake on my Olds 455, and below the heads, behind the pushrods, the block looks like it has rust or something bubbling on the block. It almost looks like dried molasses or syrup, very crystaline when scraped. I am assuming it ir rust, but how does it get in there? Also, all of the water passages in the manifold had a snot-like substance gooped up in there. I do run this boat in brackish water, but flush for 30 minutes after each run.