This is a great product. My husband has been using it for years to clean up oil spills in the garage. You simply pour this liquid on the oil slick, wait for the stain remover to dry, clean it off according to the instructions, and presto, the oil stains are gone. That said, you need to catch the oil stain right after it happens. It is much tougher to get old oil stains out of concrete.- We have never had any problems with discoloration of the concrete from this stain remover.- The bottle was leaking/seal was broken when we received it. Not much product was lost, so no return.- This product works, but still seems pricey for what it is…but it works like no other!