Where are you located?
Here in the states there is not much difference in cost between the two, so it is no big deal to buy the kit.
Look at see if the cup and wear plate are grooved and need to be replaced
Buy the entire waterpump kit. The woodruff keys are hard to get out on the Yamaha's and you'll want to remove it to access the upper driveshaft seals for inspection
Considering your time and effort, the entire kit replacement really makes the most sense....new Stainless Steel cup, gaskets, impeller, bolts, shaft key,etc. Good Luck!
