Lice321, try just putting some sewing machine oil on the knob and around it it and letting it sit there for a while. The sewing machine oil won't hurt the decals on the older metal machines, and will sometimes help to lubricate the knobs so they can move. At least it won't hurt to do it. Other than that, ask the members on the Vintage sewing machine site. They are all very knowledgeable and willing to share what they know.
Girligirl, I'm looking for some of the 'out of the ordinary' attachments for the low shank sewing machines that I can use for my Singer 99 and the Featherweight machines. I have a button holer and a blind hem attachment and a zigzag attachment. I would like to find things like an underbraider, a blind stitch braider, and other things like that. I have most of the usual attachments that came with the Featherweight machines. If you find anything interesting and it isn't terribly expensive, I'd be interested in things like that. I've been looking here in my small town, and did find a Singer pinking attachment here that I bought. It's neat to use and a lot easier than pinking shears. Thanks.