Does it ‘only’ feels as scraping the chassis or does it actually do that?

You can check if the crossfader has become a bit off in alignment: look from the side of the fader (the axis that the cap is mounted on) and see if it travels in middle of the chassis cutout all the way from end to end. If it has been in rough use and one of the crossfader (panel)screws isn´t tightened enough, it may get a bit offset leading to one end touching the cutout (and/or the dustfelt).