I just wanted to send this post to help members in troubleshooting a Brake Problem. I was experiencing what can be best described as a "sticking" brake pedal. The pedal would remain depressed at times and would need to be manually lifted with my foot after braking. The "sticking" occurred 50% of the time when applying the brakes.
I recently had the car serviced and the mechanic found that the Brake Booster was the cause. The symptoms were not typical of a Brake Booster Failure. I was told that moisture had built up in the unit causing rust.
If you are experiencing similar symptoms just consider the Booster as a culprit.
99 Boxster with 45K miles .