I swore I heard mine leaking too. I fought the temptation to cut the main vacuum line to try to get an accurate reading - I disconnected the line at both the brake booster and the pump and got very low vaccum directly from the pump. Then I reconnected the brake booster when it hissed upon disconnection, plugged both vacuum lines at the valve/splitter with new hoses and golf tees and still got the low vaccum. I wouldn't accept the problem was the 'newly' rebuilt pump. It was.

__________________
tgingrich
'83 300TD 282k
'83 300D 239k
'82 300SD 204k
DFW