I have a banjo wheel on my 39 Standard. It is a Mahogany wood wheel that I bought on e-pay. It was raw wood, so I bought some semi- gloss , high quality, boat varnish, and put about 8 coats on it, sanding between coats. That was 3 years ago. It still looks great! I believe I have seen stories where varnish is used over paint. The varnish on my wheel, for some reason, stays clean and shiney- It might solve your problem, but with a painted wheel you may want to try satin varnish. But good results, will take several coats.