Did you bench test your new starter before you installed it? Did it spin on the bench?
If not, if you can't hear the starter spin in the ski, it is likely the solenoid:
Out of the ski, hook your old starter up to the battery (ground hooked up, touch positive temporarily). If it spins, it was not your old starter.
You may be able to do the same with your current starter in the ski by bypassing the solenoid/relay and going directly to battery.
The bendix is just passive, it engages when the starter spins it out. I guess it could get so gunked up so as to prevent the starter from spinning, but you would have noticed that if you had the stator/flywheel cover off.
Bypass the E-box by leaving starter in the engine and engine in the ski and touch positive starter lead directly to battery and see if the engine turns over.
If it does, it is your solenoid.