Good morning Julian, take it apart, wash it with turpentine, put lithium grease on the bolt that drives the gear, place W140, spray lubricant, in the area, leave for a while, reassemble it, put it back and it works again, it's like I would have lacked lubrication or cleaning, since very grateful, hug
If it usually happens that something is left poorly lubricated, or the fork itself maybe worked and when lubricating and reassembling I remain as it should! Good luck, hug!