Air Bearing surfaces not coming completely clean

[[Au...]]

So, anyone have any tips on how to clean this? Isopropyl and lint free doesn't seem to be cutting it. The air bearing surfaces don't have anything that you can directly feel, but they have visible wear marks/residue. This stuff when scrubbed with a lint free cloth barely comes up, it turns the cloth black, but it doesn't really remove the streak/shiny spot on top, or the clear line on the side. I'm mainly worried that over time this will harm the machine. The other thought I've had is maybe the bearing surface is porous enough that it has kind of filled itself in with dust and oil in the pores and it's not a real issue, because it isn't abrading anything. I tried running a .00005" indicator over it and saw almost 0 movement. 

[[Ma...]]

We have something for cleaning granite, but i think those wear stains can not be cleaned. It's polished from using.
We have air filters before machine.

We had once a chip stuck in that bearing and it was grinding into granite. After replacement it was repaired - it's still visible, but no problems on machine.
In job from 2016

[[No...]]

Dirt left by something scratching over the granite surface (like an aluminum plate) tends to settle into the fine pores of the grinded surface. There's almost no way to get it back out from there, but it is not a big issue as long as it doesn't protrude above the surface. 

Edited 7 hours ago