If the shocks or struts are functioning correctly, a light film of oil covering the top half of the working chamber does not warrant replacement. This light film of oil results when oil used to lubricate the rod gets wiped from the rod as it travels into the painted part of the shock or strut. (The rod is lubricated as it cycles in and out of the working chamber). When the shock / strut is manufactured, an extra amount of oil is added to the shock / strut to compensate for this slight loss. On the other hand, fluid leaking down the side of the shock / strut indicates a worn or damaged seal, and the unit should be replaced.