I just purchased my 2016 GS second-hand. The bike is in great shape in general, but I can't easily remove the built-up, oily grime on the wheels. When I rub it with my finger, there's a noticeable residue that comes off. Can anyone recommend a product that could help? I've tried simple soap (doesn't do anything) and a Magic Eraser (worked a bit). I poked around in the forum threads, but didn't really see anything that addressed this specifically. Thanks.