^^^the other suggestions are great to try. but if you were to try the suggestiong that sweetnuts4sale stated it would be the best.
have you seen the other celica on eCelica with black painted headlights (on the inside)? if you plan on opening your headlights, it would be wise to wipe down the inner plastic and you might as well paint it. when you reseal it make sure you use silicon gel and apply it all around the headlight closure.
most likely, you have some air going through the stock glue or anoter part of the headlight itself.