A bearing seal assembly for an oscillating actuator, comprises an outer bearing raceway, an inner bearing raceway mounted concentric with the outer raceway, and an annular deformable liquid impermeable membrane having an axial length of not more than one tenth the radius thereof, an inner peripheral edge sealingly secured to the inner bearing raceway, and an outer peripheral edge sealingly secured to the outer raceway for enabling limited relative rotation between the inner raceway and the outer raceway with minimum axial distortion of said membrane. In one embodiment, the membrane is stretched to eliminate surface distortion under torsional stress. Another embodiment illustrates waves molded into the membrane for reducing torsional forces.