When rebuilding a gearbox assembly, it is preferable that all the gears and transmission-shafts are renewed at the same time.
Interfacing old worn gears with new components can lead to meshing problems and premature wear of the new gears.
Other related components you may wish to replace:
Don't forget to order all the gaskets and seals required to complete the assembly of the engine
Pro-workshop gasket sealant 08C70K0234M to complete the job like a professional.
Add as many new spares to the same shopping cart as you wish, new bearings 920450003 and washer 922001065 for example, and still only pay the same single fixed price shipping cost.