I don't think I've ever seen a 6-cyl sedan Mercedes with any sort of air/self-leveling suspension (pre Airmatic becoming option on the W211, anyway). The wagons would have had 'SLS' (Self-Leveling Suspension) standard, but, it was technically optional on sedans. Same story for W123s as well, don't know about W210s.
If the car does have SLS, there should be lines running up to a pump on the engine, likely combined with or in close proximity to the Power Steering pump. Stranger things have happened, but, I'd be shocked if it's an SLS car. Probably just really worn out springs.
That said, I did swap in some Bilstein HDs on my W211 E320 CDI - it reduced ride quality, but, made the handling much more to my liking, and I liked feeling some of the smaller bumps ('road feel') while still isolating the bigger stuff. A rather different car, but, perhaps a useful anecdote none the less. I'll throw my vote in for the 'Heavy Duty' Bilsteins, and a fresh set of springs as well. Love those old OM603 W124s - rare, good to see one with someone who gives a shit.
Semi-Sentient Centenarians
1996 Buick Century - we upgraded our crappy GM sedan with parts from a crappy GM minivan.
"It's got a van motor, a 220 cubic inch plant, it's got van tires, van suspension, van shocks. It's a model with the catalytic converters ripped out so
it'll run good on regular gas. What do you say, is it a racecar or what?" - Blues Brothers, Probably
