If you can get the small tube from the WD40 or equal behind the slot, shoot a bit of lube into the threads, might help.
But the Knurled Knobs just has to unscrew (CCW counter clockwise) a little bit to make the weight slide lighter or heavier depending on how yours is mounted.
If on the RIGHT side, moving the weight to towards the middle, less draft (-.02) on your stove, the other way towards the outside is more draft (.08+) on your stove. most stokers stove operate around the -.04. To calibrate and set it up, you need a draft gauge.