Don't know about repairs to be honest. I would try other forums for that reference and see what people recommend. Most servicing is down to lubrication, if it's worse than that it maybe something is not engaging or damage to teeth etc. Don't really know too much more than that. @Regal may be able to help??
Might need a new mainspring, might be a broken winding crown or something else. How does the crown feel when you wind it? The normal amount of resistance or does it just turn freely?
Don't know about repairs to be honest. I would try other forums for that reference and see what people recommend. Most servicing is down to lubrication, if it's worse than that it maybe something is not engaging or damage to teeth etc. Don't really know too much more than that. @Regal may be able to help??