I recently bought a great Japanese clone of the Singer 15, circa 1950. It's green and has lovely paint. The only thing marring the appearance was the ancient piece of masking tape that the previous owner left on it (to mark seam width, no doubt) for probably decades.
I posted the question-- how to get rid of it, and was told that a product called Goo Gone would work. WD40 was also recommended to me. I figured, since it was oily and I already had it, I'd try Liquid Wrench before buying another product. It worked! I wiped the masking tape with it, and then when it didn't all come off I left some LW on the tape overnight. This morning, it all wiped right off! Every bit of the tape residue is gone-- hooray!
Thought I'd share, in case someone else has some sticky mess on their sewing machine. The Liquid Wrench didn't harm the paint at all or even dull the clear coat. Winner!