I am working on a 90hp Mercury Sport Jet drive. It will try to plane off and then will rev higher and slow down. I am an outboard man but this feels like a spun hub. However, the impeller doesn't have a hub. Do the splines and grooves in the impeller go bad with time? or does the drive shaft wear out? The impeller splines look a little more worn than the prop shaft splines. Any thoughts?