depends on how bad the runout is. If it is mild, you may not notice it on light braking or low speeds, but will on hard braking and at higher speeds.Wow, 1,2,3 all pointed to warped rotors My understanding is - if a warped rotor is involved, in any given speed when braking is applied, regardless heavy or light footing, I should feel the steering wheel vibration. But in my case, only when I'm using heavy footing (harsh braking in high speed driving), it becomes noticeable.
Interesting thing is - Mercedes changed the frontend design from W126 completely. I am so familar with that on W126, in fact I rebuilt entire frontend myself on my 300SDL. Now W210 is a different animal, I have to start to learn it...
And it could be either front or rear, my experience is rear is less likely to give steering wheel shake on light braking.
Also I think all (or at least many) W210's have fixed rear calipers. Fixed calipers are much more senstive to runout since the caliper can't float with the rotor. What happens then is the brake puck gets pushed in and out by the rotor causing variations in brake pressure. (instead of the caliper moving in and out while keeping the pressure more constant) This then can cause the braking forces to vary side to side and try to move the rear of the car around. You feel that in the steering as the forces on the steering wheel vary. It is possible a stuck rear piston could give the same symptoms.
I once had a car with fixed front calipers, it was extremely sensitive to rotor runout.
Other possibility (more remote) is a tire with a broken or misaligned belt or tread. Although you will usually get a vibration that is speed sensitive as well, and it is just more noticeable as you brake.