When they designed your 550, they made the wear ring from alloy with a stainless liner. This is a pure cost saving measure; however, the down side is that when water gets into the liner and swells the stainless away from the aluminium. This then contacts the impeller and creates wear and finally jams and stops your ski from turning over at all.
Kawasaki stopped producing the liner 5 years ago and there is no new ones available!
The Wax Racing Products Pump Liner is all stainless. This means there is no liner to bulge out and jam so no prop wear. When you buy a stainless liner it’s the last one you will ever have to buy as these will not wear out.