I think that the contact is dirty underneath the mount, the contact being guided by the lever on the outside of the mount as it gets moved when the lens' aperture is changed. Did anyone ever clean this?
I would imagine one must first unscrew the chrome mount and then deal with the contact at about 1 o'clock w(hen facing the camera). Comments? - David Lyga
With the lens removed and looking at the lens mount on the camera the aperture lever is at the 1 o'clock position. It should move freely to the 10 o'clock position when pushed to the left and snap back to the 1 o'clock position when released.
Any electrical contacts with the lens are visible along the edge of the lens opening. Be careful not to bend them when cleaning. If all this is good check the battery and its contacts as the battery may be failing under load. The 3V battery available when the camera was current was notorious for testing good and failing under camera load.
If the needle is jerky when you move the aperture ring in either direction then it's dirty inside causing poor electrical contact. If it's only jerky when you open up but not stopping down the coupling may be sticky. I had the EM back in 79 brand new and it has sticky aperture coupling. I sent it back under warranty but it came back only worked a for a short time then was sticky again. I ended up selling the camera.
I've had good results cleaning these reisitance elements with one of those white pencil erasers, the ones I have are made by Staedtler and are say about 2" by 7/8" by 1/2" - it's been a while since mine were "as new' in form.