I have a similar miss in my 1990 300CE (104.980 motor).
I have exhausted all my efforts, replacing ignition components, fuel distributor, fuel injectors, idle stabilizer valve, all new vacuum lines/new tees etc.
My engine miss is much less. It is more noticeable when I accelerate from a complete stop. if I accelerate slowly, the miss is not there. I found that by decreasing the spark plug gap from 0.030 to 0.025 makes the miss go away until the gap widens.
I also replaced the camshaft adjuster as the oil was leaking through the electrical connectors.
The only thing I have not checked is the fuel pressure regulator or check the fuel pressure. Quite not sure how to do it, have to refer to MB manuals.
The miss appears to be more with warm engine and when the car is under load and it is erratic, kinda comes and goes.
Any ideas?? my e-mail is firstname.lastname@example.org