Starter valves sticking, course movements

In my ever anal effort to constantly improve my bike (6th gen) I'm doing a wax unit and thermostat. However I've noticed that the back left starter valve seemed to be sticking slightly when I manually the linkage. So much so that the movement feels course, not smooth at all.

My obvious question is what's the procedure to cleaning them up? Is there some type of bushings behind the adjustment knobs that need lubrication or replacement? And if so what is recommend to preserve the settings on the reference cyl starter valve?

I'm not at all inclined to replace the entire assembly given my objections to used parts in this situation and the awful price new. Hell, I'll get a whole engine used before that.

 

The manual advises (pg 5-73) to screw each starter valve in fully and count the turns, then loosen the locknut to remove them if needed. When you re-install, reset to the same number of turns.

I've never had the SV's out but I believe they will be similar to the choke plungers on carbs , so should be a rubber seal on the shaft that might need a little lube; maybe try some silicone spray and work the SV a few times before you pull them out?