OK, I cannot take this misinformation any longer.
I own a 1987 300TD. I do my own mechanical work.
My car has a self leveling rear suspension. I've
replaced the nitrogen cells. I hava a new leveling
valve out in the garage awaiting installation. I have
changed the hydraulic fluid. My car has the Vickers
tandem pump for the power steering/leveling system.
In short, I've never seen nor heard of a US MB wagon
which did not have leveling on the rear suspension.