Hi,
it seems that we have the same car with the same problem. take a look at my thread and see if yours is the same problem. If you have a yellow buildup its on the inside. how, i sure as heck don't know either.
I finally got fed up enough to buy new headlight housings for my '97 528i- includes lenses, adjusters, et al. They look great but were $325 each from the dealer. I looked at Angel Eyes, but appear to be in the minority that doesn't like 'em.