The guys around here ALMOST got mine right (wheel is cocked LEFT, and the tires squeal when I make tight left turns, but not right turns).
I've heard that you need to take it to the MB dealer because they need to hold something with a special Mercedes tool while doing it. Or at least that's the un-technical story I was told, anyway.

And as far as "unalignable", wear in the ball joints, and control arm/sway bar bushings, (everything rubber), can add play, but I still believe that there is a "best it will get" middle of the slop adjustment. And that shouldn't pull to either side.