Black silicone,jb-weld....Bad idea.Brake fluid will eat anything,including black silicone & jb-weld.
If you were to get silicon in your brake system you would have more problems then you have now.
wasn't sure about the JB Weld, but I'm pretty sure that the silicone would swell up eventually,lose contact and start polluting the brake system as you mentioned.
I would probably take it back off and clean it up real good and fill the rust spot up by building it up by welding (with a welder) and grinding it back smooth...just another idea...
