I have a 15-91 that I'm cleaning up for SIL. Got it at an estate sale. I know it came from a smoker's house cuz I'm getting all kinds of yellow gunk off with the Goop cleaner. That's on the machine. However, looked at faceplate of machine and it is yellow also from tar & nicotine. How do I clean that up? Open to helpful suggestions - have checked Bily's cleaning tutes and didn't see where he covered this. Thinking Brasso or silver cleaner perhaps?? Looking for ideas, please.