So to bring coolant level up is water okay, or do you need the special MB coolant?

 

distilled water is fine

 

Yeah I'm not sure with some of the MB stuff, for all I know it was some sort of waterless coolant. Its the step sons and I try to avoid it all I can. I'll fix broke, I just don't need the blame breaking it.
With these cars a simple spark plug change could turn into a many month deal, unless you wish to spend every waking moment working on it.

 

Oh don't worry about that, coolant is like...50/50 is by the textbook, so 50% water and 50% coolant which consists of anticorrosion/antifreeze, but I'd probably go as far as saying that 30% coolant / 70% destilled water is still fine and won't cause any problems