I had a thread on here back a couple weeks ago about low vacuum. It's since gotten worse. If I'm stopped at a light with my foot on the brake, within about 10 seconds all my vacuum assist is gone and the brake light (low vacuum) comes on. About 3 seconds after I take my foot off the brake, the light goes out and the assist comes back. At idle I can fully press the brake pedal once. If I release it and immediately press it again I have very little if any assist, the pedal is VERY hard. I've traced a lot of the vacuum lines and can't seem to find any leaks anywhere. Is there any common failure of vacuum system components I should be aware of? Is the booster dieing a slow painful death? How can I test the vacuum pump or the booster? Thanks in advance

 

Simple way to test for vacuum leaks is to run the engine for awhile, shut it down for a few minutes then disconnect any vacuum line.
You should hear a hiss. A system without leaks will hold vacuum for hours if not days.
If you don't have any leaks it could be the booster itself.
If you do have a leak next step is to buy a simple vacuum pump with gauge and start isolating lines individually.