The carbon seal is what seals the driveshaft from leaking water into the hull, where the shaft goes thru the hull into the jet pump. It would have no impact on RPM and Power.
The wear ring is in the jet pump where your impeller is and is most important for having a proper clearance with your impeller, so that water is sucked in and forced out properly and efficiently. It wouldn’t really impact your RPMs, but definitely impacts the power potential of your ski. It wears out with time and sucking debris thru the impeller and wear ring.
it sounds like you have an issue with not being able to get the engine to maximum RPM. If you haven’t changed the spark plugs recently, do that before you do anything else. Many times, that solves the issues for just a few dollars if you can do it yourself.
