Renewing all the wear and potential wear components during a transmission overhaul will attain the best results.
Interfacing old, worn parts with new will lead to premature wear of the new parts and compromise long term durability, smooth "rifle-Bolt" changes and ultimately, reliability.
Other components you may wish to consider to aid you with a successful gearbox overhaul:
Add as many items as you wish to the same shopping cart, new thrust washer 92022112 circlips 9203302592033029920331037 & bearings 92046031 for example, and still only pay the same single fixed price shipping cost.
This component will almost certainly have other applications within the Kawasaki model range; please check the part-number is right for your machine prior to ordering?