That machine is likely to have a cracked camstack gear, and be frozen up with old oil. They were a great machine in their time, but claimed to be a non-oiling machine. If you can imagine a machine that didn't get oiled hardly at all, and the dried up tar that develops from it. I wouldn't buy it. I've seen too many in the shop with cracked camstack gears and that were too frozen up.
My go-to vintage machine is an old Kenmore with a front-loading oscillating bobbin/hook. They're just a tough workhorse machine. I can usually find them for less than $35.