I've had a mini-disaster with the C63 yesterday. Oil filler cap came off, and coated the engine bay with oil.
I say mini because of two redeeming factors:
1) The cap was still sitting on top of the engine when I looked.
2) The oil level post-disaster was still on the MIN mark, so I was able to drive home.
What a bleeding mess it's made though. And when I stop after a journey, it's smoking a lot because there's oil on the manifold.
I've cleaned off the top fairly well, but I can't get at anything lower down. debating whether to get some engine cleaner, work it into what I can get at, then (while praying mightily) gently hosing it off to hopefully somewhat clean the lower regions too. But rather worried about the potential to screw up electrics.