Speedo works, odometer doesn't.

[Silver Fish]

I have carefully removed the speedo today to see if I can work out why the odometer is not working.
The symptoms are: speedo works well and is not bouncing, odometer reset knob is not working, and the trip meter is not working either.

I have removed the drive section where the speedo cable connects and if I turn the little brass cog and shaft on the top right in the third photo then the odometer works perfectly. Therefore my problem lies in the drive section with the magnetic wheel. I suspect the shaft with the worm drive is not working or connected and I can't see how to get this piece apart?

Does anyone know if I can get a replacement worm drive shaft for this or is it time to box it up and sent if off for repairs?

PS I have read the ESR and pelican posts but can't find this issue.

[9er]

It can be fixed at home if you open it up and see the gear that needs to be replaced and order the correct one.
I take mine to a guy in Strathalbyn and he does it all for me.
Obviously you can post it to him.