My first time servicing a 7758. Started to open the mainspring arbor and was surprised to find what appears to be a small gear affixed (permanently?) to the bottom end of the arbor. Feels like some kind of Teflon material. I assume it drives the moon phase wheel? Any help here would be greatly appreciated. Not sure how to proceed since if it isn't supposed to be removed from the arbor I'm not sure how to deal with the spring.