I have sort of a similar problem with my 1979 300CD, where it would shake but it also wouldn't really go at all until it warmed up. I took it to the transmission shop and they told me it was the tourque converter. It started out doing the same exact thing a few months ago and then one day it got bad. My advice would be to take it to a good transmission shop who have worked on a few Mercedes, and see what they would say. My shop didn't charge me anything to inspect the transmission.