Change the oil and look for metal bits in what you drain. If so, you need to take apart. It should spin smoothly when in neutral. That might just be that the cables are not adjusted and it is dragging though.
There are 2 needle bearings in the AB gear that are the first thing to wear out. Once worn enough, the AB gear can flop and drag other gears. It is worth a gasket to take apart, clean and check things out.