I took the glide off - I'm not sure it's made much difference, but I'm still checking this out (I need to do some more testing).
I did yet another cream wool berber last week. There was dark (black) stuff in-between the loops. I tried really hard to agitate this out and extract it. In the end I tried agitating with a stiff hand brush - which lifted it to some extent, but this grey/black fluff/dust was really hard to move as it was bound up with the carpet fibres, deep in the carpet.
My process: Vac'd -> pre-spray with Cleansmart Split-X -> Agitate with Sebo duo and a hand brush -> extracted at 135psi with a stair tool.
Anyway, I did my best; but today I've been recalled to do it again. So, does anyone have any suggestions to clean this carpet better?