4) Make sure your bearings and knife-edge are clean and in good condition
Make sure you haven't moved the beam forward or backward enough to let the axle rub against the agate V brearing retainer clips. (Mostly likely the problem.)
Clean the bottom of the V bearings with a sharp toothpick to make sure there's no dust or grit in there, then clean the knife edges with a tissue. DO NOT oil the bearings or knives and DO NOT attempt to secure the V bearings so they can't 'float' into perfect alignment.
Insure there is no spider web in the slot where the copper vane on the left beam end goes.