Unknown fluid leak not gasoline

Have 1999 Taurus Wagon and discovered oil based fluid stains in the inside area of rear passenger tire. Short errarnd 4 blocks produced floor stains on floor inside both rear tires. Fluid does not smell but visual inspection of undercarriage showed leak staining tank. Any ideas as to what this?

Thanks in advance

Have 1999 Taurus Wagon and discovered oil based fluid stains in the inside area of rear passenger tire. Short errarnd 4 blocks produced floor stains on floor inside both rear tires. Fluid does not smell but visual inspection of undercarriage showed leak staining tank. Any ideas as to what this?

Thanks in advance

Check your brake fluid resorvir level, sounds to me like your brake clyinder could be leaking. Make sure your brakes are working before driving so you are not surprised when attempting to stop quickly. Remove the wheel and brake drum and inspect. ( I assume it has brake drums)

Check the brake line and fitting too. The leak may be external (not within the drum) if its getting on the underside of the floor in the back.
You may have a rust hole in the steel or flexible line, or a loose fitting thats allowing fluid to spray onto the underside of the floor in back.