Well, my first recommendation would be to find the correct forum for the Mercedes Benz 300D.
Having said that, I am unable to comment further, as I (and probably every other guy on this CB750 forum) have little or no experience with your particular problem.
(I know...I'm a smartass...forgive me, Lord)
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.