An easy way to check out any vacuum operated system for leaks is with a smoke machine. You can plug (or T it) it into any hose in the system, turn on the smoke, the entire system gets pressurized, and the leak (or leaks) shows up quickly. It produces less than 1 PSI, so nothing gets hurt. Most auto repair shops have one, so if you have any problems finding your leak, it can easily be checked.