It's often easy to repair a vintage machine, but not (in my opinion, anyway) if it's a broken gear.
There are vintage sewing machine groups you can join if you want to try to take the machine apart and fix it yourself. Personally, that is way more than I would want to do in this situation, but some people enjoy the process. Try joining the vintagekenmoresew group and the oldkenmoresewingmachines group at groups.yahoo.com . Also try the wefixit group. There are a lot of old sewing machine guys on those groups who can explain what to do.
If it were me, I would donate the machine to Goodwill (labeling it with painter's tape so buyer knows it doesn't work; dealers often buy these machines to either fix up or use for parts). I understand the sentimental value, but sometimes new is actually better.