Hello bass community. I have a used 90s Peavey Fury I bought last year. Amazing instrument, however I can't get a few set-in thumb prints to come out of the butterfly tuners. I tried chrome polish and lots of elbow grease but they just come back. Is there a certain acid or solution I can buy to remove them, and make them look new again?? I thought about dipping them overnight in jewelry cleaner but wasn't sure if that would make it worse? Any suggestion would be so helpful. Thanks.