well if any thing is leaking you need to replace that part. they only work if you don't have a leak. to get the air out. you first make sure you didn't lose the fluid in the reservoir. if you didn't then you have to start from master cylinder and get the fluid there. if you never lost fluid then its easier. after changing the problem leaky part. stop on the brake pedal and build up pressure. and another person open the bleeder on the back of the wheel cylinder or caliper and then when your foot is to the floor have the person close the bleeder. repeat pumping the brakes and open bleeder. then check the fluid level. don't let it get to low and start sucking air. repeat a few times till there is no more air coming out the bleeder.