Yeah. The weird thing is I can't think of any ferrous metal in the block or in the cooling system. My other thought is maybe it's not rust but just dye staining. Mercedes coolant is orange.

BTW, you'll be pleased to hear that I'm flow testing everything and car is going to get as much breathing as I can give it. I just wish there were a way to give it more of an intake manifold to work with.

 

So you don't think it's from the head gasket itself?

 

It's a carbon head gasket with a built in silicon bead. The only metal I see in it are rights around the top of the cylinders. Or does the carbon matrix have a ferrous metal within it?

 

Using 1500-2000 grit sand paper isn't going to take off enough metal to make anything no true anymore.. unless your aggressive with it and sand in one spot aggressively then it can eat the metal.. when I worked at the shop the engine builder always used a find wiz wheel on aluminum and steel blocks to clean corrosion off them and never had any issues.. even does it to his $5000 aluminum heads on his 598ci big block race motor when it was freshened up a week or 2 ago..

 

always just used a green scrub pad and some motor oil and will be ok. clean with brake cleaner. dont agressively scrub it, just average pressure.
why not get the block decked?

 

Why deck a perfectly good block? That fucks up all the clearances. The wasn't a head gasket repair. Heads and intake are just out being modified. It's already running high-comp pistons, I'm not keen on decking the block.