I got my new ( DVAP sent another, free of charge ) head yesterday, and brought it in today. It is not visibly cracked, and in resonably good shape, showed signs of burning a little oil, and running rich, but other than that, seemed in good shape. it did/ does have the replacement type expanding freeze plugs ( the nut you tighten, then the rubber expands holding it in ), when I pulled the 1st out, I got clued in very quickly, that radiator stop leak had been used, it needs to go, it's grey and hard, just like stop leak gets, but, it's very bad, the inside ports are almost fully blocked off from the stuff. what will eat this stuff?