You need a new bleed valve. It has probably been damaged from over torquing or worked itself loose. Try tightening the bleed valve, as it may have possibly worked itself loose somehow. The only purpose of the rubber cap is to keep the bleed tip clean. It would never and could never hold back the immense pressure from the hydraulic brake system of your car.

If tightening the bleed valve does not work, go buy another one. They are pretty cheap. Simply unscrew the old one, and screw in a new one. I believe I saw a set of 4 on ebay just a couple days ago. But I recommend going to your dealership and picking it up.