I think it's generally referred to as the valve cover, though Mercedes might call it a cylinder head cover. I dunno?
Anyway, pull it off and remove the baffle and baffle gasket inside (3 or 4 phillips screws). take it to a machine shop and have them put it in their cleaner. It'll cost about $20, but it will remove most of the old paint and get the oil out of the metal.
When you get it back you'll find that the casting is not that good of a quality, with numerous defects and wrinkles. Use a flat file on the flats and dremel or die grinder with either various barrel sanders or cylindrical stones to get in the rounded areas.
You can get engine paint at an auto parts store or maybe a hardware store. I tried to find a high temp primer but was unsuccessful there so I just used the paint. Read the labels on the cans carefully, it should hold up at 300°+. Mine has been holding up okay but I'm noticing a few small blisters afer only about 6 months. If I had to do it again and had a few extra bucks I'd get it powder coated. Some people have the aluminum polished for a chrome-like effect.

I'd get a new gasket as well, if it hasn't been replaced in a while it will likely be stiff and provide a poor seal if re-used. Even a new one can be kind of touchy and prone to leak if it's not set just right. torque it down to spec, over or uneven tightening can cause a leak in a short time. You'll need to replace that gasket for the baffle too (cheap dealer item), use a good thread lock on the screws (maybe get some Benz stuff from the dealer while you're there). You might also consider putting washers under the cover bolts as the twisting directly on the paint will scrape it off under the bolt heads.