Sounds like a hole in the booster membrane. Someone else would have known this, and that's why they removed the vaccuum line. Make sure that you have the 1-way valve in the line to the vaccuum source.

Go to the wreckers and try find another one. Otherwise see if a brake place can "recondition it, by getting a new membrane. I don't think it costs that much from memory, and they should last 20 years.

Chris