Bought a 2001 XR Honda the other day. It's in good shape but was stored in a barn. The seat has black spots/stains on it from mold or ???. I attempted to clean it with a brush and soapy water with little success. My next step was Bleach White which worked a little better but the stains are clearly still there. Other than the stains the seat is in great shape so I don't really want to replace the cover. Suggestions?