+1 on that - if the odo stopped working it's likely just a $9 gear. Could be the sender or associated wiring in the diff rear cover too.
I have a few spare "parts" clusters and I'm willing to split them up if you need parts. There are very few differences between any e30 clusters. Is yours a VDO or MotoMeter cluster? It'll say 'MotoMeter' in the center if it's the latter.
PM me for advice if you feel so inclined.