Climate Control Vacuum leak?

[Eric Eliel]

My '84 300D developed a vacuum leak....door locks started not working and then the car wouldn't shut down. Classic case.

I traced all the lines, checked all the usual door elements including the fuel tank door and truck lock with the Mity Vac. Check all the under the hood lines and the vacuum shut off lines into and out from the dash. The transmission etc. blah blah blah.
Vacuum pump is pulling 23" btw.

I have at this point sealed off the bright yellow vac line running from the rear of the ROUND vacuum check valve into the passenger compartment. The other line leads to the main vacuum tank.

So the car will now shut off. But I don't have pneumatic door locks and I don't think the climate control pods will activate the doors.

Since I checked all the door elements, I think the climate control system has a leak.

Where is the usual suspect? What area is prone to breaking hoses or leaking? (I'd also like to know where the climate control branches off from the door locks, can't seem to find that on the schematics).