Need a W126 speedo for replacement.
 

Next problem: A little tiny plastic gear that drives the odometer is broken. There are three gears and it is the smallest. The easiest thing would be to replace the speedo section of the cluster. Where can I get a used one? Mine has 178000 miles. Also a outside temp gauge and the 2"X6" piece of molding on the passenger side rear fender would be nice. Ideas? TIA

I could send you the speedo out of my 1988 420SEL parts car. It has about 173k on it, pm me if your interested.

Go to W>W>W>odometergears.com. they have the gear you are looking for.
If you are in there go ahead and replace all three gears. They have a set of all three. The one large gear with the small gear on the back of it needs to be the one for your model. Count the teeth on the small gear on the back of the big one, this will be the one for your model cluster. You can just buy the single small gear if you wish.