If the two-way switch retard system is working properly then all good, but if not you really don't loose much without it, but you have to adjust . I choose to disable mine because my speed switch was wonky and the retard was being cancelled irregularly.
For others that may read this: The retard system exists solely to reduce low RPM emissions and works only at less than 2500 RPM and if the engine is in that operating temperature range of not stone cold to less than 100C/212F.
Benz Dr. is a recognized authority on these vintage Bosch distributors and we have had spirited discussions that taught me all I know about these 061/066 retard style distributors. The mechanical advance curve is adequate by itself for good drivability, but if you have no retard you have to re-set your idle speed.
I am not an expert and I am sure there are some aspects of this system that I do not understand when it comes to versions of this car with automatic transmissions. My manual shift version is more tolerable of a higher idle speed that comes with no retard/two way switch but I was able to successfully reduce the no-retard idle speed and the car runs wonderfully.
I think I will budget a 123 Ignition distributor with programmable advance curve settings so I can mimic the 051 distributor pulling vacuum from behind the venturi flap. I really like the idea of how the 1968-9 M130.980 was set-up to run with vacuum advance/retard. I believe it was the pinnacle setup before emission restrictions forced compromises. With the ability to retard timing a degree or two on the fly I won't have to worry if I have to run 89 octane fuel.
Also, I had recommended to me a thermostat for a diesel with a 3mm hole drilled in the rim as an ideal thermostat for an M130.980. When engine temp dips below 170F the thermostat will close to a reduced flow position.
