I purchased a 5 year old home. The garage floor has a nice gray with black and white speckled coating on it. The previous owner had a large rug on the floor. When I removed the rug, I discovered 4 Brown stained areas from tires where a car was parked. I have tried every product I have to remove the brown stains (windex, comet cleanser, soap, and goo-b-gone, using a stiff bristle scrub brush). Some of the stain appears improved, but the majority is still there. It can be scraped off with fingernail, but ouch & way too much area to cover! Anybody have an idea what could cause tires to leave brown stain on garage floor coating, and how to clean it off?