Denso starter 428000-3150 or 515 176 103 has 08 teeth small engine starter motor. Skidoo discontinued and replaced it with 515 176 585. The new replacment starter motor is 09 teeth. Now the question is does it interchange? Yes, we have sold and have had no issues. The reason there is two different gears is the gear ratio. Both will mesh with the flywheel.
When replacing a starter its a good idea to inspect the ring gear on your flywheel to see if it needs replacing. They do get worn out over time.