I have a Rivet leather saddle on our tandem. It worked pretty well last summer, but this summer it has become super slick and shiny, I'm guessing from the consistent application of chamois lube, and I can't seem to stay put on it. The tandem is a custom made bike, and I've had a professional fitting from one of the best fitters in Seattle, so I know the sliding isn't because of improper placement of the saddle. Is there something I can put on the saddle to make it a little less slidey without ruining the finish? any pointers from you leather lovers?