Well, I committed a classic mistake in troubleshooting and jumped to cause when I discovered an issue with the defrost vacuum pod. While that pod was indeed bad, it was not the cause of my overall vacuum troubles. It turned out that I had a bad vacuum pump. Vacuum was just fine right at the pump but would begin to tumble as I added circuits. I eventually located a good used pump (from a forum member) and once that was installed my vacuum woes disappeared. I surmise the original pump had a weak check valve that was fine under no load but would give up the ghost when enough vac circuits were added.

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Joe

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1980 300SD - 495k miles - 'The Ambassador'
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Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD