I wonder if anyone can give me any advice on cleaning old sewing machines that have gone yellow with age and sunlight? I've just bought a 30-year-old machine that's in great condition, but unfortunately the housing has gone very yellow in places. It's only on one end and along the top, so it's apparently the effect of sunlight rather than smoke or any other kind of dirt. The affected parts appear to be painted/coated metal rather than plastic. I haven't yet made any attempt to clean it.

I know about whitening yellowed plastic using peroxide hair developer, and placing the item in the sunlight inside a clear plastic bag, and I'm planning to use this method (when we get some sunshine again!) on the plastic carrying case, which has also gone yellow.

But what about the machine itself? I wouldn't be keen on covering it with the peroxide cream as some of it would be likely to seep inside around the edges; and the whole process of putting a very heaving machine inside a thin plastic bag without tearing it, and then leaving it in direct sun, seems pretty doubtful to me. Or am I supposed to take the machine apart (not tried that before), and just treat the affected sections separately? Would it even work on the metal parts? Or is there something else I can use?

I've tried to find information on this online, but not discovered anything specifically about yellowed painted machinery (as opposed to separate or easily removable plastic parts). Any guidance would be very much appreciated!