Thanks, Paul, for the very informative answer. I'll have to take another look at the shutter now that you've explained it. I figured out the "pull the cord" part and the release bar, but never quite finished working out the rest of how these shutters worked.

Somehow I thought I recalled a dial with speeds. That is what really had me confused. As I said... I'll definitely have to have another look. Your description of "T" and "I" is more like I imagined it working!

The rusty axles might end up being the major problem. I'm guessing that if it's only surface rust I can clean and polish, but if it's worse maybe I'll have to attempt replacing them. I'm also thinking that the holes they fit in can be bushed with brass, if they aren't already, if the holes are worn.

You just may have given me the courage to tear it apart and have a closer look. Thanks again!