Hello Dakotamaid,
What a great machine! We very rarely see Davis vertical feeds here. It is the one American machine I would like to have a go on.
I have had a good squint at the pictures. The discoloured metal, especially the bobbin winder, looks like a residue of dust and oil. This should come off easily with a bit of persistence with metal polish. The stuff I use is called Peek, made in England (hurrah hurrah) and is obtainable in the States. If you can't find it in the shops you can buy it online from
http://www.tri-peek.com It goes a very long way. I am still only halfway through a tube after cleaning about 10 machines. Make sure you don't let the Peek get onto the japanned area of the decals, because it could lift off the top layer of the decal. If there is any stubborn oily residue on the japanned areas or decals, try a little bit of undiluted washing up liquid (ie. for dishes) on cotton wool or a soft cloth. Once dust and stubborn residue has been shifted you can wipe the black areas with machine oil on cotton wool.
Miriam - Thanks again for posting the links!