Your question about the use of unleaded fuel is easy to answere:
All Mercedes-Benz cars (pre-war and post-war) have absolutely no problems with unleaded fuel.
We recommend to use fuel with an octane rating of 98 (ROZ) for every type and also a regular control of the valve clearance, twice as much as specified by the factory. In our experience no additional lead substitute additive is necessary.
A normal use of the car is required, of course.
We hope this will help , please feel free to ask if you have further questions.
Mit freundlichen Grüßen /Kind regards
Mercedes Car Group
Mercedes-Benz Classic Center
000/R051 - MK/CL
Phone: +49 (0)711 / 17 -8 40 40
Fax: +49 (0)711 / 17 -8 34 56
Stuttgarter Str. 90