I got my new (to me) Hampton Carryall today. It's in pretty great shape overall. I've done one treatment of Leather CPR that has helped the dryness a lot but I'm wondering about how to deal with the handles. They are stiff and dark, nearly black in some places - this is a British tan bag. I did scrape my fingernail across it to see what would happen and it looks very much alike I got up a layer of dirt. Whats the best way to get layers of dirt out of handles?