MMI Screen Gear Wheels...Again!

[Bisonhead]

Sorry for dragging this up again, I know you will be sick to death of posting the same old links!!

I have successfully taken out the MMI unit and will be stripping the motor out to get access to the gear wheels.
My questions is, if only one wheel needs replacing, can I simply replace that one. Also, where is the best place to get a replacement? My first thought was a scrappy but you lot are the knowledge!
Cost is an issue unfortunately so no sending the entire unit to the US for repair or any other crazy £400 fixes!

Thanks!