So trying to get the green monster to shutoff on its own, crawled underneath the dash and checked vac. at the shutoff switch. On the brown/blue line I have 5in and dropping when I turn key off. On the other line I have 20in steady with engine running - no drop? I think I need a switch. What do you guys think?

On the line from the ignition switch to the shutoff valve you should have 0" of vac when the car is running, and when you shut off the car it should jump up to around 15" of vac and then bleed back down to 0" quickly after the engine is shut down.

It sounds like the shut-off valve on the ignition is bad.
Here is the shut-off valve on the ignition switch. - http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1L00T87R028I0OQRRI&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1979&product=D2020-11741&application=000015943

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