There are many incarnations of the cruise amp. over the years as MB has improved/modified it. The part # (on the alum. case) that I gave was for the one I had in my hand at the time, just so you would know which one I was referencing. I've taken out many of these by contorting and loosening the 10mm. bolt. It is NOT 11mm. in any I have ever seen (which is many). You were probably on the welded nut; the bolt hex head is on the other side (in a recess that you won't believe, push some rubber stuff slightly to the side and feel into the recess with your pinkie). You will be undoing it blind, but it IS 10mm. (deep socket helps). If you can put a box end wrench on it (or even see it) you weren't on the bolt, but on a nut welded to the bracket. That's why it wouldn't turn.
The Golden Rule
1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)