Ive had this same problem and after 10 valves (that DID NOT want to adjust to where I want them), a broken 13mm bolt that holds the linkage on and 3 hours I finally threw both my wrenches at the concrete (causing them both to shatter into a total of six pieces
).
I still haven't MIG'ed them back together yet. There really is something amazing about breaking things when your pissed at your mercedes...
