The first question is what OEM make is the cluster/speedo? It will be either a VDO, or more unlikely a Yazaki.
The difference can be seen by looking at the speedo dial faceplate. A VDO has no divisions on the trip odo between the hundreds of miles with just one between the hundreds and tenths. A Yazaki has divisions on the faceplate on the trip odo between all the hundreds and tenths of a mile.
You haven't said what part of the speedo is not working. Just he odo/trip odo, the speedo needle, or both?
It is possible for a competent amateur to fix certain faults themselves.
See Dave Barton's website for some guidance on the odo fix:
http://www.240turbo.com/740-odometer-repair.html