I, personally, would not get WD-40 any where near any of my sewing machines. It needs to be cleaned off if used.
I would probably polish with a Dremel polishing bit, or just a t-shirt. Since you have the bits off the machine, alcohol could be used. I like alcohol swabs for getting old oil off metal. You don't want to get alcohol on the black or decals.
Janey - Neat people never make the exciting discoveries I do.