More two steps forward, one step back...The good news: with the aid of the above photo, I freed my stuck vent door.
The bad news: when it freed the spring thing flew apart. And doesn't look like it wants to go back together. One step forward, two steps back...
Got the linkage for the face vents reconnected and all seemed fine - briefly. Then I couldn't get flow at the screen demister and when I looked at the actuator not much was moving. Disconnected the face vent link thinking it is binding (or I re-assembled it incorrectly - probable) and the actuator is moving again in line with mode selector. It also moves when the blower setting is changed. Is that normal? Is it merely the air flow pushing on the doors - or something more sinister?