dont pour nothing inside the headlights! cuz then it will leave water spots. my headlight has a leak and when moisture gets in i stick a hair drier to dry it off. it still leaves water spots. your only choice is to buy after market head lights. this yellow stain sounds like the headlights are old. and there is no way to make it clear again. its like buying white shoes, when they are new they are super white and bright. then over time they get yellowish, faded, dull. there is nothing out there that can rejuvenate back to its original condition. .