Hi, I went to tighten my headers today, and bam. There was fluid over my spark plugg wires and the headers and the head.

I have had driveability problems and can not do burn out. I get stuck at 1000rpms when i powerbrake and floor the car. So, first of all I put the cap over thinking that that was the problem. However, the fluid seems to be coming out just a tiny bit from the underneath the first piston (I am not totally sure). Its where the plastic meets the metal coming from the booster. Sorry, never really worked much on master cylinders and such before. I was just wondering if this could be causing a vacum leak or not!??
Also, there is a bit of air coming from there when I press the break.
Should I replace it!?? And how hard is it to replace! I assume not that hard, but is there anything special about changing it!?!?