I pulled a vacuum on the booster, I can hold 28 inch vacuum. With a vacuum on the booster and depressing the rod (booster out of car) I can feel air blowing out around the rod grommet the section that's in the interior. I'm likely replacing this anyways just curious as I always had a rock hard pedal and not much stopping power

 

You can have a leak through your booster when the pedal is pushed or unpushed or both. If you pump of vacuum to the booster and it holds, when you press the pedal it should drop a little then hold, say 10" lower than it started out. If it goes to zero you got a leak.

Charlie