When we lifted carpet from our oak flooring, we discovered dampness (dog urine) and black mold spots. After using varnish remover and 60 grit sandpaper, they still remain. Are there any solutions to removing these spots and darkened areas? Where the floor is worn also has black streaks in it. We do plan to use an oil based polyurethane finish. Would just like to have it perfectly new after so much hard work.