A combination heat exchanger comprising of a heat exchange core having a plurality tubes, wherein the core having at least one core end; an end tank having two side walls and two end walls, two bulkheads the cavity defining a least a first chamber, a second chamber, and a third chamber, a perimeter edge defined by exterior edges of said side walls, exterior edges of said two end walls, and exterior edges of said two bulkheads; a header plate engaged between said end tank and said core end; and a gasket between said perimeter edge and contact surface of said header plate, wherein the compression ratio of the gasket is varied along the contact surfaces of the perimeter edge and contact surface of the end plate.