"Sticky" F2A Feeler

I bought an F2A from a local source on Friday. I played with it in the shop to check the meter operation, but as the shop isn't exactly well lit I only used the lens close to wide open.

In trying to use it today, I ran into a problem. Somewhere around f/11 or so, the feeler will get "stuck" and will not spring back when moving the lens past this point. Once the tab is stuck, it needs a gently push to past f/11 or so, where it will then snap back to the rest position(or the set aperture on the lens).

I pulled the front off the finder, and don't see any obvious areas that need attention or anything obvious that's causing it to bind. The tab is guided by a plastic(nylon?) pin riding in a metal groove, and of course I'm inclined to think that the use of plastic here would have meant it wasn't intended to be lubricated.

Can anyone offer any suggestions as to what to do/where to check on where the problem possibly is?

THanks.