Do not want to replace brake vacuum boost canister. There is a rubber boot on the shaft of the brake pedal under the dash. It has a few indentations/openings that looks like there is a reed/flap below which seals when the motor produces a vacuum for the brake booster. It is leaking sometimes there w...

Have intermittent vacuum hiss at brake pedal...slight touch makes it often end. Starts again after some use later.