A face seal assembly includes a first and a second metallic sealing ring having a common center axis, and each including an outer ring surface and an inner ring surface. A non-metallic sealing element is positioned upon the outer ring surface. The metallic sealing ring also includes a sealing face facing an axially outward direction and extending circumferentially around the center axis in a path that varies from parallelism with a plane normal to the center axis. A stiffness relief groove extends inwardly from the inner ring surface and circumferentially around the center axis and forms an annular spring zone of reduced material thickness to compensate for the varying of the path of the sealing face. One machine system application includes a final drive in a ground-engaging machine.