I wouldn't use polyurethane on an antique machine. The shellac would be the way I would prefer. Both seem tedious and need patience that I don't have. That probably is a real good machine. I know Miriam has a machine that looks like it was "rode hard" but not put away wet. She was quite happy with the way it sews.
I think I would probably just wipe it down good with sewing machine oil and call it good. Should I want to do something a little bit more protective, I would use some car wax. I know it is recommended that a carnauba wax be used and
https://singer-featherweight.com/products/zymol recommends and evidently sells Zymol. I have seen it in auto parts stores and Walmart may even have it.
Janey - Neat people never make the exciting discoveries I do.
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