All wear ring waer that is what they do. They wear due to impurities in the water such as suspended solids, sand small rocks. Remeber the seadoo works like a giant vacume cleaner. So to compensate the wear ring sacrifices itself as opposed to the impellar failing.
To change the wear ring takes some specific tools. (unless your lucky) but for the most part the componets will be set faily firmly. You will need a toll to grasp the shaft and unscrew the impellar, then you will need to take out all the bearings, oil(expensive and very specific) . When all of the drive is out then you must cut a slot in the wear ring using a dremel tool. (chizel can work but you risk cracking the fiberglass housing) . After you have the old ring removed simply press in the new ring. )(tip put the new ring in the freezer overnight. it will be smaller and easier to press in) then put the whole works togethter.
Get good and changing the wear rings because they fail often.
you can apply as chemical agent that bonds to the plastic wear ring but not to the impellar. The chemical adheres to the side walls and fills all of the damage. It actually can improve your top speed because the tolerance is reduced to zero. This saves removing all of the components.
Look for the product on Ebay under seadoo wear ring.