Better late than never
Attatched is 2 photos of an S54 failed headgasket. It always fails between the cylinders, and for whatever reason its always between 1 & 2, and 5 & 6 that fail first.
Bizarely on CSL's they seem to fail between the other cylinders as well, where as standard M3's just seem to go between those end cylinders (In my experience, this may not be the case across the board).