Oh, it has been awhile since I had mine apart. First of all, the pittman arm won't change the wobble in the drive wheel, unless something is really off. My cone screw took a few tries with the new grease to settle in. What I am not remembering and causing me a bit on concern is the dark areas near the widest end of your screw. I thought mine has a shiny even taper all the way. Your dark band may have been caused by a century of wear. But don't freak out. I am going from old memories. Someone may have a more recent experience. And maybe even pics.