Since it is not super black, assuming you did not clean it, it might just be a surface crack and is not letting gasses escape? I know the manifold on my LS was pretty putrefied looking in the center like that, but it was not leaking any gasses that I could tell. Looks just like grey iron around the area, and no carbon, unless it is just burned off. Do you recall hearing an exhaust leak? It would be pretty noticeable if it does leak.