Black ebony finish problems

I have an upright piano with a high-gloss ebony finish (lacquer, I guess). It's not an antique yet -- it's 40 years old -- but I'd like it to be an antique some day. I definitely want to keep this piano: I've had it since I was a girl. I must have cleaned it with the wrong thing at some point in its life (an alcohol-based cleaner?) because now, whenever I try to clean it with conventional furniture polishes, black comes off on the cloth. It's like the finish is coming off on the cloth even though the piano is still quite black and shiny except for smear-y residue in some places, which I'm afraid to clean for fear of hurting the finish even more. I've wondered whether the black that's coming off is 40 years of accumulated polish/cleaning products/grime. Whether it's finish or grime, I'm afraid to do another thing until I know what I'm doing.