@ Diesel:
I measured directly at the pump even with the closest metal line removed. Next, I pulled the check valve (22mm socket) and it did have some gunk but easily cleared. I reinstalled the check valve & re tested. Vac was still 8-10" unless the engine revved.

I've read threads where pumps failed for various reasons and am not looking forward to tracking down internal engine parts to repair. I'm contemplating getting a compression gauge as that also needs to be checked as a step in figuring out what is causing an engine shake.

Vac pump repair kits are apparently NLA. I've seen a few on Ebay at ~$170. I'd buy a new Pierburg pump at that price and keep this one for parts. I may have kept the old one somewhere.

Current thoughts are to: 1. run compression test while vac pump is installed so I have compression information on engine health. Right now I only know that it starts easily with 1 glow even at temps in the teens.

2. remove and disassemble the current pump before deciding the next step.

I have a parts car available but want to keep that engine complete without scavenging parts.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.