The adage “they don’t make them like they used to” goes double for sewing machines. The owner of my local (non-specialist) repair shop looked at me like I had two heads when I asked if it would be more economic to buy a new sewing machine rather than pay to repair my mother’s that she’d gotten in college. He had quite a few functional treadle machines on display, and the prices weren’t anywhere near Antiques Roadshow, just what you’d pay for something high-quality.
So no specialist needed.
Well thirty years ago we used to have a singer repair shop in a town about 30 miles away. It’s gone now, so I’ll probably have to go a ways to find a repair shop these days.