When rebuilding a gearbox assembly it is preferable that all the gears are replaced at the same time Interfacing old worn gears with new can lead to meshing problems and premature wear of the new gears!
Other gears that may be required:
TIP: Fit a magnetic sump plug to catch the tiny shards of metal that are removed from the teeth of new gears when first engaged! See if this part fits your application: 90013230810