Also, don't get too wrapped up about the ceramic washer issue. It's an easy replacement that you could even do yourself if you have basic mechanical ability. The metal washers aren't cheap, but I wouldn't let ~$100 in parts separate me from a deal if I was happy with the boat and the price. Even if you have to pay someone to do the labor on it, it's not too bad.
If you or the current owner can pull the SC off, you could verify if the current washers are ceramic or metal. The ceramic ones I've seen pictures of have looked green, but a sure-fire way to tell is to use a multimeter and do continuity test. Continuity = metal. I bought my '08 used and had the SC service thrown in, so I don't know for sure if mine were ceramic or not. I've understood that all of the jet skis for '08 were metal, but the switchover on the boats was later (mid year) because the boats didn't have the issue nearly as much as the skis since boat owners typically don't come out of the water and free-spin the impeller. (It's going from loaded to unloaded to loaded that creates the slippage and wears down the washers and eventually caused the ceramic ones to fail.
If you check the last 4 characters of your Hull ID Number, you'll get the month and year it was made. The first character is a letter representing the month, where A = January, etc. The second digit is the year. If your boat was made before May '08, it probably has the ceramics. May would be 50/50, and after May, as I understood should be metal. But the real way to know is to actually see.
The quick things you'd want to be able to check are:
The wear ring (around the impeller) - check for grooves that may have been caused by ingesting debris. Any significant grooves will reduce thrust and performance. The part is not expensive (~$30), and could be a DIY replacement.
The impeller - make sure it's in perfect shape.
RPMs - you should have no problems hitting 8100 RPMs in the water. If you don't get to 8100, you have slippage in the supercharger and it's time for a rebuild. With only 21 hours, the only way that would happen would be through abuse. Lots of boat owners have gone much longer than 100 hours between rebuilds (not that I would recommend that), as boats aren't nearly as hard on the SCs as the skis are.
Make sure all the basic stuff works: all the boat switches and lights, trailer lights and so on. Make sure the pole for the stern light is in the ski storage locker. I think your model has a bow filler cushion as well.
A
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