Thanks to 'forced induction' and 'wheezy 83' for their comments. While I rebuilt the pump with a kit, (no diaphram in my model), the cause for loss of total vacuum was due to the check valve located in the small threaded piece which connects to the flex hose going to the brake booster. If I would have checked this, I would have saved a lot of time & energy in not removing the pump!

Hope this helps someone else.

This is a great forum for all of us diesel nuts.
Last note: I filled up this am and paid $4.40/gallon, at the lowest price in town! Yikes.