I think one of the most important parts of the page you linked should be highlighted:
WARNING. This shoulder bolt has a nut on the back side. If this nut is not removed, and a big screwdriver is put on the shoulder bolt to turn it, the shoulder bolt will shear. This renders the shoulder bolt useless. If this happens nothing short of ordering a new shoulder bolt from Pinball Resource (part# a1059) will fix the problem. So the moral of this story is to first remove the nut from the shoulder bolt before removing/adjusting this bolt. (And even then during nut removal sometimes the shoulder bolt still shears.)
Before disassembling the whole unit, I would loosen that shoulder bolt, clean the pivot point (http://www.pinrepair.com/em/gtbcred1.jpg), etc and make sure the lever moves freely. I've found a lot of steppers that were completely non-functional only needed a bit of care at that one point.