Dave -

Unfortunately, cruise control problems are not unique to the W107, and
cross several model series.  A dealer can only sell you more of the
same.  However, a company called General Development Laboratories in
Goleta, CA has developed a very profitable business repairing & selling
replacement components for your cruise control.  They seem to be the
Gurus.  I recommend you seek them out and go sit at their feet for a while.

You can reach them here:  http://www.gdl-online.com/begin1.html

Successful self-repair is also possible, but not for the faint of heart.
I got lucky, but don't think I would attempt it a second time.  While
I've not personally utilized GDL's services, I've heard nothing but good
feedback about their products from other MB owners here on UseNet.

Jerry Wolfram
'78 450 SL - 214K miles

Get the part number of your crusie control amp and see if there's any on
ebay.  The amp should be under the dash on the driver's door side of  the
steering column.