I bled my brakes a few months ago, and they got much better. Slowly overtime they started feeling more like they were before. I looked at the brake calipers and noticed the front left and right rear calipers looked like this around the bleeder screw. The others were completely dry. I tried tightening them, but they would not tighten without first loosening them. Is this how air is getting in my brake lines? The fluid level has not changed. How can I prevent this from happening again? Were they not tight enough, or do I need to replace the bleeder screws or put sealant on them? When I bled them, I got them about as tight as I could with a 11mm smaller wrench. When I bleed the brakes again, do I need to do it twice while activating the hdc/tc system between?

 

Bleed screws have cone shaped tips to do the sealing. The screw threads are not what seals. If the cone tips get buggered up or rusty, they won't seal and should be replaced. Try to get the 11 mm (wrench size) replacements (not 10 mm) otherwise easy to mix up/round off. I suspect the cone tips can get damaged by over-tightening. Be prepared to part with some coin for new bleed screws, but minor cost in the grand scheme of things.