I'm not an expert on alcohols, but etanol and metanol will damage shellac, and likely gum up the presserfoot shaft worse. Alcohol will dissolve the shellac, make it gummy and liquid, before it dries again. I'm not sure what isopropyl alchohol does, but for parts in connection to the black paint be careful. Spray can oils like WD-40, Weldtite Teflon spray doesn't (but can harm gold decals). Basic sewing machin oil does the job too, it can take a bit longer but tentantive applications of basic sewing machine oil and moving parts will eventually flush out dirt and grime.