On the advice of this forum I bought a MityVac and checked the vacuum system on my 1980 240D. Looks like I have a leak somewhere in the door locking system. But I also noticed that the engine shutoff valve will also not hold a vacuum. Is that normal or should I replace it?

The shut-off valve should hold a vacuum. Does the engine shut off when when you apply a vacuum with the Mighty-Vac?

Sixto
95 S420
91 300SE
87 300SDL
83 300SD