The Mercedes part catalog calls it Control Unit / Actuator. No mention of Vacuum. The early models used vacuum.
My 2008 Edge and 2004 truck must be old. I can accelerate to the speed I want by by keeping the cruise button increase depressed.A quick shout out to Kris AKA @JamesDean for solving my non-functioning cruise control. I shipped Kris the speedo, module, and actuator and in a very short period of time he identified/fixed the issue and returned everything to me. My mechanic, Tom, and I replaced everything, and voilá, CC is working great! I highly recommend Kris if you have CC issues.
Now I just need to go cruising on a nice road trip! I'm really going to enjoy the accel/decel control, which strikes me as having been ahead of its time back in 1985, although my cursory google search yielded no verification of when the first accel/decel stalk appeared. Maybe someone else knows?
Another interesting observation: I noticed that my accel/decel stalk works differently from any modern cars I've driven. In my experience, in modern cars a nudge on the accel/decel stalk (or buttons) changes speed a pre-determined interval, i.e. ~2 mph, and no more or less. By contrast, in my SL I simply hold accel/decel as long as I want until it reaches the speed I want, at which point I let go and the speed is maintained. I actually like this better, as I can nudge the stalk just once to reach the desired speed, whereas on modern cars I must nudge it multiple times to reach the desired speed when the desired speed difference is greater than the pre-determined interval.
So there are my cruise control thoughts for the day.