Welcome!

I agree with Jeff on the fluid flush. Do a search -- I described the procedure twice in the past few weeks.

On the "adjustment" screw. It's not really what most people think it is -- ie, a "remover of slop in the wheel". It changes the amount of contact between gears inside the box, changing the amount of effort one exerts on the wheel to turn it. The slop stays there, you just grow bigger forearms moving the wheel around, hence the perception that it's "better". Some imprecision is inherent in the design.

best, whit