Here is a vacuum diagram that might be easier to use for the shut off specifically:
http://www.peachparts.com/shopforum/attachments/diesel-discussion/121864d1401410079-how-does-w123-shutoff-system-work-vacuum-diagram-engine-shutoff-plus-may-14.jpg
Your going to need a MightyVac. The first step would be connecting it directly to the shut off valve and pumping.
My intermittent problems went away just by replacing all of the small flex portions. It cost ~$10-15 and sure saved a lot of time. Look at any vacuum line near the oil filter, as they get disturbed more than others.