Amsoil is a great lubricant. There are also many great alternatives at Walmart priced very well. I use Amsoil in some of my toys.
My JeT skis live a much harder life than most of the tow vehicles on this forum. One is a Turbo Charged Honda with 546 hours, and some mods to up the boost. No problems to report. The other one is a Supercharged Seadoo with only 100 hours, but it's been solid so far, and the Supercharger design is somewhat fragile on those. The S/C works using Wet Clutches. I believe Amsoil has helped in that area.