I would not try a used one. The plastic gears wear out and the replacement used unit you're considering is already 24 years old. I've had several speedos and odometers rebuilt at reasonable cost and they look great. I've used these folks with excellent results:

http://www.speedometershop.com/rep-pag.htm

__________________
Steve S
Support Tech
UnwiredTools, LLC
www.unwiredtools.com

1982 380SLC
1994 E320TE
1998 E300DT