Udate: All is well... opened up the mounting plate and one of the 4 bands that were sitting in a groove had fallen out of there. Put it back into the grove and the aperture preview lever moves freely now. But it makes me wonder: I was expecting 4 ball bearings. Might a previous repair job lost the ball bearings and the person substituted them with 4 bands? This is an earlier model from what I can see (the serial number starts with 200) maybe this was the mechanism back then?
Anyway..time to put this lens to work!