Oh! The 758 that KittyWolf has is a Self Winding Bobbin too. I have one here, it's plastic, but it doesn't seem -too- bad. It hasn't been run through its paces yet though. I'm waiting on feed dogs.
That's the other thing to watch for. About that time, Singer started putting rubber feed dogs in the area where you oil.
Not the best idea, but I understand there was more reason than just selling replacement parts. Some of the stitches required fabric to move better than steel dogs would allow. Another thing to watch for though. These rubber dogs deteriorate, and won't feed fabric. They can be replaced, and they're fairly cheap (the 758 for instance uses dogs 181843 and they're about $10. It's a good bargaining tool)