What the article means is that you should connect your vacuum tester to the black vacuum line that goes from the connector at the vacuum control valve back to the vacuum modulator on the transmission -- the idea being to test that part of the system for leaks. It shouldn't leak. Again, look for the black vacuum line.

The vacuum control valve, though, is all about leaking. It leaks off vacuum at a controlled rate to modulate shift damping based on throttle position.

Have you tried isolating the vacuum system managing the engine and transmission from the central locking (yellow lines) and climate control (blue line) systems? If not, that's the first thing I'd do. Unhook the accessory lines at the big connector at the firewall, plug the holes in the connector and see if the car shuts down properly.