A seat adjuster assembly includes an electric motor having an output shaft with a worm gear positioned in a gearbox, a spur gear meshing with the worm gear in the gearbox, a spindle shaft fixed to and driven by the spur gear coacting with a nut contained in a tube, and a linkage system connected to both a vertically movable upper vehicle seat part and a non-vertically movable lower vehicle seat part that positions vertically the upper vehicle seat part responsive to the position of the nut relative to the spindle shaft. At least one washer is provided on the spindle shaft. The spur gear is a plastic spur gear molded over the washer. A pair of leaf springs disposed in the gearbox bears against the spur gear and a wall of the gearbox.