Seems all that is left to check is whether the transaxle speedometer drive is actually turning, and whether the speedometer itself works.
Jack up the car and put it on jack stands. Disconnect the speedo cable at the speedometer and route it so you can see it. Start the car and run it in gear. Does the inner cable turn?
Yes, then check the speedometer.
No, follow the cable back until you find what's causing the inner cable not to turn. Common faults:
- worn inner cable ends
- inner cable too short
- angle drive issues
- worn plastic speedo drive gear
Speedometer, spin its drive with a small screwdriver. It should flick one way but not the other. Flicks? Hook up a drill (turning the correct way) and run it up. No flick, pull the speedometer for repair.