I got a unit from Autozone for $79.95 for my 83 CD.
It is made my one of the Japanese radio company's, vacuum operated, with magnets attached to the drive shaft.
It works ok, a little slow to engage but holds the speed well.
I left all of the old parts in place and just added the new unit, the only thing I don't like is the push button control, you can't use the Mercedes stalk.
Jerryb