Installed aftermarket cruise on 1993 300D
 

I installed an Audiovox vacuum-operated CC in my car last week and I am very happy with it.

The parts to fix the orig CC would have cost about $300 + rewiring the PO's mess when he tried to fix it. The CC was $100 delivered. Took a half day to install (mostly the wiring issue - I could do one in 2-3 hours or so now I think). I used the car's VSS and did not need to mount the included speed sensor. I also wired into the car's CC stalk, based on what I learned from this forum.

It holds the speed within 2 mph and works about as good as the original. There is a setting for "low power" cars that makes it quite responsive.

It even does something the original couldn't - I can tap up or down in one MPH increments using the stalk.

It's not rocket science - if you can do basic mechanical and electrical stuff, you can install one of these. The directions are pretty good and there are loads of different ways to fit cables. Audiovox is completely useless as tech support though, saying that it is not designed for any Mercedes models.