What kind of shape are your lower ball joint and the guide rod mount in?

On my SEC the guide rod mount made/makes some interesting noises once it got pretty worn, as well as shuddering when turning at slow speeds.

edit:
I just re read what vehicle you're working on, after having mixed it up with a w126 I was just reading about.

I don't know if your car has anything equivalent to the lower suspension mountings of the w126 cars, but I'd check there, since you seem to have taken a good look at the brake system already.

Best of luck!

__________________
-Josh
Testing the cheap Mercedes axiom, one bolt at a time...