I have seen this issue a few times. If you are also a Honda Engine dealer, contact your distributor and see if they happen to have a parts engine lying around that you can get the flywheel and starter from. The Honda k1 series Horizontal and Vertical shaft engines use the same flywheel.
This issue arises from the fact that the flywheel actually comes to a stop in the same position, over and over, which eventually causes the starter ring to wear. Replacing the flywheel and electric starter will resolve your issue.