Yours might have a small electric motor to control the odometer, my car
has one. Its bolted on right next to the wheels with the numbers, its on
the inside of the cluster so you have to disassemble the cluster  Or
your drive gear might of stripped out.

When I was pricing parts for mine when the trip meter died the only part
GM sold was a gear. Any other parts or service needed you had to send
out the cluster, then a certification sticker has to be affixed to the
inside driver door that says the speedo was serviced on such & such date
& this was the mileage at that time.

Should be easy to find a cluster in the junkyards to match yours, but
then you have to worry abut the accuracy of those gauges

  Harryface       Ø¿Ø
1991 Pontiac Bonneville LE
          302,552 miles