An UPDATE.. Mercedes' mechanics shared their knowledge. The Steering Rack can on be adjusted once in its lifetime. The rack is set to a specific pressure point (my understanding it is for calibrating steering stiffness, not being too light or too stiff).
The rack needs to be removed from the vehicle and place on a jig.
The yellow plug is fitted, and the gauge takes the measurement through the hole in the plug. If the pressure nut (on a metal disc) is moved or removed, Mercedes-Benz state the rack will now have to be replaced. ( to me, it sounds quite a stretch as to say it needs to be replaced, I think it should be recalibrated instead to my opinion). I have been trying to adjust the nut pressure pint till I think it got close to the manufacturer. If the nut was tightened lightly the steering will feel WAY to lose and not comfortable on a higher speed, if the nut is too tight, you will have steering wheel harder to turn, you need to catch the middle so to say.
Also, on this similar subject, if one noticed, while driving straight, and letting your hands off the steering wheel, the car starting to go slightly to the left ( in the UK). A Mercedes mechanic said, if the car ‘pulling slightly to the left’, lots of people book in for alignment and then complain after that the car still pulls to the left ‘they didn't mention it before the booking’
This is due to the camber of the road, tyre wear, and Mercedes do pull slightly anyway to avoid oncoming traffic should you drift off. So with those things combined it will always sometimes pull worse than others depending on what road you are on etc. So if you hold the steering wheel straight ahead, and you drive straight your alignment should be ok, if for some reason you let go of the steering wheel it will go left.
However, if you hold the steering wheel dead straight, and it's going left, so you have to hold it slightly right to go straight, then the alignment is slightly out, and you need to have an alignment done.
