Um, it's the opposite actually. Sorry if I wasn't clear.

I disconnected the vacuum line from the v.m., plugged the v.m. end and put a vacuum on the line. It holds great, so no leaks in the line.

Next, I put a vacuum directly to the v.m. through the fitting the vacuum line ordinarily connects to, and it won't hold any vacuum at all; instant leakage.

My 1-2 shift is nice and firm, but I get flaring on the 2-3 and the 3-4 shifts. I'm managing to work around this with judicious modulation of the throttle, but it's one of those things that needs to get fixed. All of the downshifts are perfect, it's just the last two upshifts that aren't quite right.