For what it's worth, guys:

I use some motorcycle hydraulic fluid I had acquired for my son's motorbike. Perhaps even hydraulic jack fluid would work; that's generally available even at your friendly Wal-Mart store. If later models call for ATF, that is what I would use.

The MB maintenance manual I have calls for the linkage to be dismantled, cleaned and relubricated at each oil change. I suspect that is part of what is supposed to be done with the flat rate hour or so MB allots for oil changes. My personal observations of dealership workshops indicate that it is generally not done.

I do my own oil changes and, thus, the linkage cleaning (I use Q-tips) and lube. My car is now 21 years old and the linkage shows no sign of wear or other deterioration.

The following is purely a hypothetical opinion: the only detriment I can think of resulting from using grease is that the cruise control has to pull harder to activate the linkage. I have seen failure of the cruise control to work traced to dirty gummed up linkage (not my car).

My $.02 worth.

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Ted
1979 240D
165,000 miles