Hello harvo

A warm welcome to these forums.

I think I understand the issues here.
You have a Rover Auto-Drive, a copy of the Greenfield design.

Parts Lists may be found here:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php/topics/7306/Rover_Ride_On_Information.html#Post7306

I think your link depicts an incorrect sprocket.
My reading is (best guess) this:-

Sprocket: A12327
https://www.outdoorking-forum.com.au/index.p...arch_in_description=1&keyword=A12327

Chain: A12335
https://www.outdoorking-forum.com.au/ride-on...ckets/genuine-rover-primary-chain-a12335

Rear Axle Assy: A10336
https://www.outdoorking-forum.com.au/index.p...arch_in_description=1&keyword=A10336

[Linked Image]
[Linked Image]

Hope this helps.
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Jack