You might have a broken shock or a broken or sagging spring on the driver's side. It probably has somethng to do with the suspension.
If the shocks have not been replaced in 131,000 miles and after 18 years, it is time to replace them. The springs and the spring pads can also be replaced. There are some bumper gizmos that go on top of the shocks, as well. Perhaps it is one of these that has decayed and fallen off, as they are made of some sort of plastic.
I replaced the shocks on my 300D, and it is not a really difficult or specialized job, I suppose any capable mechanic could do it. The springs will probably need to a compressor to remove and replace them.
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"