Well, this sucks (Ha! A vacuum pun!) - checked out the last of the things-that-use-vacuum in the Chevelle this evening after my plans to mow the lawn were rained out (again... going to have to bale it at this rate). Put the knock-off mighty-vac on the line that feeds the interior (HVAC) and... nothing. Could pump all day and it held no vacuum.
Guess the dash gets to come apart.
In other news, the brake booster doesn’t leak (which is good since it’s basically brand new) and the vacuum modulator on the transmission (and its line) also are leak-free. That means the interior is the only thing still leaking, unless I’ve got a bad gasket somewhere.
I’m tempted to disconnect the interior line and cap the T until I get the chance to pull the dash pad off. The weird thing is the controls inside still lead to creaky-vacuum-pod noises when you move them around with the engine running, so it’s not 100% open. Just leaky somewhere.