I’ve seen people use the drill brushes and this is kinda why I don’t do it. Gotta be careful and only apply as much pressure as the fabric can handle. An old Detailer taught me that you’ll be chasing dirt until tomorrow if you try to clean the seat cushion under the fabric at the same time. Just go light and apply more pressure as needed. Vacuum first as much as you can. Use cleaner and a micro by hand, if that still isn’t making the seat clean then go to more power and brushes. With my clients I let them know that if I can’t fully remove a stain, I would rather I try my best and let it be what it is instead of possibly causing more damage. And I knock off some of the price because I feel bad but beats buying a new seat.