Have you tried to look at it yourself? Bobbin winder on my vintage (1965) 503 Singer quit so I was winding on a 99 which was set up. DH was trying to fix another problem the 503 had and when he had the top cover off, he adjusted something and bobbin winder worked after that.
It was a couple of years ago, so I can't remember what he did, but a gear wasn't connecting (obviously). Also found a lot of lint that we cleaned out! By the way, this Singer has never been to a repair shop despite lots of use. It was my Aunt's. DH is my handy man and I'm keeping him!