Are you sure the gasket is fully seated on the pan? I changed the fluid and filter on my 500E recently and while refilling, I heard a dripping sound from under the car. Probably half a quart had spilled on the ground because the gasket had dislodged from it position on the pan on the passenger side creating a big gap. If there is room you may want to see if you can slide a feeler gauge between the case and the gasket.