You can buy the proper tool from the Mercedes dealer for about $20, made by Hazet, I think. It has to be long in order to fit through the holes for the cam bearing caps. I would NOT cheap out on this. Buy the proper tool (and not the Made In Taiwan stuff, either), clean the bolt heads, and make sure the tool is fully seated before you start really cranking with a breaker bar. You do NOT want to strip the heads on these things.
If any of the heads are damaged, REPLACE THE BOLT. They're only a few bucks each. A lot of people replace the bolts every time the head comes off, but I think that's overkill... there is a spec in the FSM, if they're within spec with good heads, I re-use them.
