Thanks, OldMe. There must've been changes in E-Series or some of the postings are for other Ford vehicles. The pic in your link shows the vacuum line coming out of upper right and servo horizontal. Ours has line at lower right and servo vertical. Same Marque, Same Problem. Shame on'em putting those parts so inaccessible. I was reluctant to do much poking around inside that HVAC cabinet. I do know that when I pulled the grommet out, it was only a few inches till something hard and too large to pass through the hole hit from the inside. I figure that was the check valve.
An auto electric guy told me to figure out where the electricity (or vacuum) source was and where it needed to be. Don't try to trace, just connect those two points. I wish I'd painted "ACME" on the reservoir. That label has fallen off. Thinking of Wiley Coyote helped me get through the project.