I've noticed lately that i'm losing pressure in my brake peddle. I checked the inside of my front driver side tire and it is covered in brake fluid. The rubber cap over the bleeder was popped off so I simply pushed it back on and filled up the brake fluid to the appropriate level and the cap continues to pop off and I am still losing alot of pressure in my brake peddle. Is there something i'm not doing? And if so, how do I do it?