I've noticed this a few times, but I wrote it off with the W124 being new to me.
Over large waves in the road, the kind which force the suspension to compress and extend a good amount over a relatively long period of time, they're not bumps, it's kinda gentle...anyway, when transitioning from compressed to extended and normal again, I've noticed the steering wants to pull a little bit.
I played on a stretch of road I know well, and not holding onto the wheel, it moves a little, but always returns to pretty much where it started.
I chalked it up, initially, to the suspension's movement changing the steering geometry enough to feel it, but I know Mercedes engineers aren't going to make a totally rookie move like this.
With 150K+ miles on it, the front-end is likely due for new tie-rod ends, new struts, many new bushings, and the like, but is this a symptom of something worse than just getting old?
The tires are worn, and before I replace them, I plan on new wheels, many new front-end parts, and a proper alignment. However, if this truly odd steering behavior is an indicator of something bad, I'll take care of that before I start commuting 70 miles per day.
Thanks!