Anybody know of a new source or substitute rebuild kit for a Quattro Coupe rear driveshaft universal joint?

Thanks for reference to the right part...goodness knows why I said differential.

Now I'm looking for a local source for a KV engine timing belt.  18mm wide, 120 teeth, trapezoidal.  Seems sinple enough but despite following up several listings, I havnt been able to find one. 

something like this?

https://store.034motorsport.com/center-driveshaft-cv-joint-for-audi-quattro-vehicles.html