I am looking an FX140 to buy it and the engine has 19hours on it. It has been run in salt water but there is very little corrosion on the exterior of the motor.

The shop (a marine repair facility that really doesn't work on waverunners) has it on consignment from a customer. The story from the owner is that the ski would fail to start once a season, but after charging the battery it would finally bump over and run fine all season. I suggested to the guy who is working on it to take the seat support off, access the coupler and try to spin the output shaft to see of the motor was locked up (without the plugs in, of course). He did this and tells me that the engine will turn over with the wrench and becomes free for part of the rotation then gets "stiff" again and requires the wrench to "get past the stiffness". He said that the customer brought them the ski not running, told them to "winterize" it and he would deal with it in the spring. I asked how they winterized it without it running and they said they "poured" antifreeze into the flush fitting (nice...). With this information, I am willing to still buy the ski, but don't know what typically happens to a motor when it gets anti freeze in places it shouldn't.

I suggested further that they take the motor mounts loose, slide the motor forward, and then try to turn it over without the coupler engaged as the coupler bearings could be the root of the issue? Has anyone heard of the bearings in the coupler get stiff enough to keep the engine from turning over? As I said, looking at all the engine components, the inside of the hull has seen very little water of any kind. It really looks like a 19 hour machine (the multifunction meter will turn on long enough to show it) The spark plugs are black but show no signs of water or rust.

I think that there are three distinct possibilities for the issue from best to worst:
1. The coupler bearings are trashed, keeping it from turning over
2. The owner injested water or towed it or something and the head has valves that are trashed and that is where the "resistance" comes from.
3. The head and one or more piston rods are "comprimised" and this is why it seems to "hang up" through part of its rotation.

Any thoughts? I obviously can't tear it down as it does not belong to me (yet) but if the motor is completely trashed, I have to budget for the long block in order to make an appropriate offer. Thanks for any suggestions for diagnosis techniques or experience with similar symptoms.