We just installed an old claw-footed tub in our new house. The finish looks to be in excellent condition, however, when we take a bath, there is an oily brown film that covers the water, then coats the tub when drained. It's not in the plumbing-our other new tub is fine. The tub doesn't need a new white finish--it looks good & shiney. Is there a clear product that needs to be used?