I dunno how far I can help you, since I really haven't tampered too much with the W140 in our garage. However, from my knowledge, http://www.bekkers.com
DOES sell replacement lens for the '95-'99 W140, so your lens MUST be removable...if you can somehow find out how to remove them, and then clean off the inside, then I think you should be good. I think somebody else on this board can help you in that respect. However, if you REALLY can't get that white film off with cleaning, http://www.bekkers.com
seem to sell USA replacement lens for your S-Class (W140) for either '92-'94 or '95-'99 head lights at $89US per side, so you can always go that route if all else fails. Good luck!