I have to admit to using soapy water in grimy cases, but leon is right, if the shellac is worn decals will suffer. Shellac can take a well wringed up cloth, but it's important it doesn't leave any dampness. The same for polishing these machine, it works great, but be careful when going over the decals, if there is a good layer of shellac over them it's safe. Tiffany decals are very decorative, colors and swirly guilding like no other.
I don't know how you manage with bobbin tire and winding on that one, but I guess it can be sorted out.
SewClassic has a clever way when it comes to measuring drive belt. Direct download
here if it works.