It's starting to look nice again, great job :- )
I've had good results with resin polish like Auto Glym, a regular brand in the shops here. There are lots of equivalent products in stores. They polish and further lift up dirt and grime, and leave the machine shiny like it once was. However, as you know well, decals are delicate and can stand up to a cleaning and polishing if the shellac finish is in good condition.
Is it a rotary model? If the hook and race turn in one direction it is, some models are occilating. If it's a US made rotary model it might take
this type, but you need to measure accurately or verify in some way. Japanese made machines tend to take class 15, if it's made else where usually not, unless it's Singer of course.