As "Troon" has just pointed out to me, this is for an NTG 2 style machine.
It was from my brothers R class. I'm not so familiar with this stuff, but it is for a DVD system, not a DX CD as in my W203 C-class (unfortunately!)
"Might help to make it clear that this is for NTG2. It won't, for example, suit my S211 DVD nav. See here:
http://mercupgrades.com/COMAND+APS+FAQ-faq-10.html#17"