You have a bad vacuum on the intake manifold? Reverse pressure?
http://www.hoppers.com.au/basics.htm
Maybe if your engine has 'blow-by' that the pressure could be blowing the oil backwards? (Maybe.)
Master Cylinders Make Pressure
To apply a hydraulic fluid pressure to the brake calipers, we use a master cylinder, in essence small pistons connected to your brake pedal which generates fluid “pressure” according to the force applied to it and the area of the piston by the formula.