So the guide it self does not show “what to clean”. Only the replacement.
BUT!
If you’re confident you could clip off the shield that hold the ball in place + the 4 little rollers (that are magnetic, so be aware of that)
The rollers are having 2 parts. 1 magnetic part (black) and the grey ribbed roller part that is actuated by the ball.
That ribbed part i cleaned of all 4 with a microfiber cloth. And one of them (cant remember which of the 4) was really stuffed with gunk (dust and other stuff)
And I learned the hardway that the position of rollers matter… So potentially you can accidentally flip X and Y axis.
Edit: Found This reply that did the same thing.