[Patrick]

When I deflect the vane (power off) with a toothpick, it returns quickly to center.

Since your vane is moving smoothly this might not help but here is info on the new and old style shadow meters. Like morzh I was thinking possibly weak magnet.
https://web.archive.org/web/201607271921...ctip01.htm

I had a copy of those tips. Strong magnet, coil not open. But I didn't remove it from the circuit and test it with a variable power supply. I should have done that first. I'll try it now.