The best way to find Rotax part numbers is to use the parts lookup @ BRP, @ https://epc.brp.com/
Select “Rotax Engine”, then drill down via your engine model. (The model of your engine is designated on the engine tags that came with it new, and can also be found on the engine plate attached to every engine.)
There is a guide in the group to assist with finding your engine model, guide is located at:
https://www.facebook.com/groups/ChaparralVortexBoatOwners/posts/2424795411159530/