If Spray 9 does not clean it - it was not meant to be cleaned! Well, maybe too strong a statement, but we have used this product in house for 20+ years and it remains our g0-to cleaner. If Spray 9 and a brush does not remove the dirt or stain, we don't know of any multi-purpose cleaners that will. Great for any area of the boat! We do use on upholstery with a soft brush and it will remove years of grime. Just be sure to rinse the upholstery with water after cleansing.