Outer Limits 4x4 Board

Well as i had a post up not that long ago about in the search for a brake booster i was feeling around the gasket between the booster and master to find the leak was coming from under there. Went and bought some gasket paper and goo pulled them apart to find the air that was coming out was actually coming out from a small groove at the bottom of the master cylinder. Just wondering what this groove is and why would air pressure be coming out of it......

THe booster is a large diaphragm. It needs to let the air out the gap when the pedal is applied, the diaphragm moves forward and if the air can not get displaced it wont work or be pushed into the master cylinder. it should only be blowing air when the pedal is depressed if its leaking all the time then you may have a leaking diaphragm.