Professional engine builders replace inlet and exhaust valves, springs inner and outer, valve guides, retaining cotters, seats, tappets and retainers as a matter of course when carrying out a cylinder-head overhaul.
Also the valve train itself requires close examination, the condition of the camshaft lobes, cam-chain, tensioner and guide should all be considered when overhauling the top-end.
The valves and the interfacing components have a tough time and can become brittle with age and wear. Broken bits of metal are not too good for the engine!
Other cylinder-head and valve train related components you may wish to renew at the same time as this part:
Don't forget to order all the seals, gaskets and new fasteners required? Add as many items as you wish to the same shopping cart, new retainers 12009005 Spring seats 160071024 and collets (keepers) 12011004 for example, and still only pay the same single fixed price shipping cost. This component may have other applications within the Kawasaki model range.