The basic setup for the locks is as follows:

Vacuum is drawn by a fitting at the back of the intake manifold. There is a combo fitting there. One line, secured by a banjo fitting runs down to the trans. Leave this one alone since your tranny is OK.

On top of that fitting, there should be a rubber hose that connects to a plastic line that runs over to the driver's side to a bunch of connectors near the hood hinge. You will notice a line that runs back across the firewall to va vacuum tank under the right fender.

There will also be a yellow line, which supplies the passenger door/trunk/gas locks (elements). This runs to a valve in the driver's door. The valve has connections for the "lock" and "unlock" side. When you turn the key to "lock" the valve applies vacuum to the lock side of the elements, and vice versa for unock. The lock/unlock of the driver's door is mechanical.

The two vacuum lines run from the valve in the driver's door to the pass. door, then to splitters, and to the trunk lock and gas door. The gas door may have only a "lock" side, with the unlock handled by a spring when the vacuum is released by the door switch.

All of the elements have rubber diaphragms that can crack and cause leaks. The valve in the driver's door can lose its seal. The fitting where the line enters the tank can dry out and leak.

I suggest that you start by removing the panel on the right side of the trunk. You should see where the lines from the pass. door branch to the rear elements. You can connect your mityvac and test both sides of all three elements. Lock has a red stripe; unlock a green. Connect the mityvac, pull a vacuum on both sides to what works.

Have fun!

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe