I can't tell for sure from your picture, but in looking at the schematic, I'm pretty sure the factory removed one tooth from the Player unit ratchet gear to prevent it from advancing past the 4th player.
And in any case, a missing tooth wouldn't prevent the Player unit from resetting to player one. If that's what's happening, the unit is probably dirty.

https://www.pinwiki.com/wiki/index.php?title=EM_Repair#Step_Up_.2F_Reset_Stepper
http://www.pinrepair.com/em/index2.htm#steps

I looked closer and it looks like the factory removed that tooth from the Player unit ratchet gear to prevent it from advancing past the 4th player.

pasted_image (resized).png