fails a catostrophic death and so take a look at and follow these links which explain how the booster is put together and how it works:
http://auto.howstuffworks.com/power-brake1.htm
http://auto.howstuffworks.com/power-brake2.htm... etc
The above has good graphic illustrations to help in understanding. The article even talks about how diesels have a separate vacuum pump. The booster costs over $300 so I would first concentrate on ivestigating the check valve where the vacuum line enters the booster shell, and the "O-ring" and "Pinion" seals that are located at where the master cylinder bolts onto the booster... where the rod protudes from the booster.
Good luck,
Sam