Yes, that advice seems correct...that pot is BURIED on the chassis...and tough to adjust with game on....I am always afraid of getting zapped when I reach my hand in there...take off your ring if you are wearing one!
Yes, like Todd said it's buried in there in a REALLY bad spot. The one you took a pic of is NOT the adjustment. This one is a small white knob, like the other white ones. It sticks straight up off the board.
Just think, you were ready to sell it, and in less than a day now you're back in business 100%. Those little nagging problems that are minor are always the worst damn ones, I think i'd rather have the thing be completely broke them have something minor that acts up constantly.