See my post (and the related answers) on 4.10.01 (try link
W126 - front suspension noise
I replaced the lower ball joints and the guide rod mount (kit is part no #126-330-13-35) -- also known as castor rod joint -- and it solved my somewhat similar problem. Labor at an independent was $260 for both ball joints (I did both sides) and $260 for both guide rod mounts. Dealer labor would have been $316 and $308 for the same work. Parts were $25 each for the ball joints and $62 for the guide rod kits.