The plastic used for these apparently is very easy to break off, which isn't surprising. I finally decided it was time to correct that, so came up with this relatively simple solution.
I used 3/16" square brass tube from a model shop, which is the same size as the square section of the original lever piece (seen in pic above). I found metal rod that fit into the square tube tightly. Measured for length and bent the rod at an angle as the lever "handle". The metal rid is slightly smaller in diameter than the original plastic piece, but not enough to affect usability.
Put it all together - using epoxy to glue the metal rod into the brass tube - hopefully that holds up long term.
Reinstall and presto! Vents that now open and close!
Just make sure that you get the rod "handle" in the correct position before you epoxy it together, otherwise your handle could stick out at a funny angle and/or not open/close the vent properly.
No pic of the finished install yet, but I also plan to add a press fit washer to the end of the rod to hold it in place. I also haven't trimmed the length of the handle yet - it's a bit too long in the pic above.
Someone with a lathe could turn these out of square stock so they are one piece but I don't have a lathe...yet.
