I replaced all four of the shocks on my 1990 300D with Bilstein HDs. It improved the ride greatly.
The reason that i did this was that the front tires were showing signs of cupping. There were no symptoms in the rear.
All four shocks were still pretty stiff when I removed them. I took the shocks off an 82 Buick Regal once that were easier to squeeze shut than a concertina, though not so musical.
The new shocks also seemeed to have raised the car a bit, because now the spoiler no longer rubs on the same parking lot wheelstops as it did before.
I described the whole procedure on this site, by the way. You will need a bottle jack and some other weird tools to get the shock in position.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"