What Red said. Bleeder screws are open to the elements, water goes in, and rust forms. I ALWAYS pack ALL my bleeder screws with wheel bearing grease after I finish bleeding. That way no water can get in there.
If only I would have read this yesterday...that does make sense though to pack them with a little grease. I did repace them with 4 new bleeders though. Next time I will be sure to remember that little tip about keeping the elements OUT of my brakes..
