The brushes are almost certainly graphite, which actually isn't a metal.

Also graphite is diamagnetic, so strong magnets actually push it away.

Since we're speculating, the brushes could also be some harder material, with Carbon Nanotubes impregnated, or graphene infused and coated, etc.

Also, although I don't have the numbers for your issue about strong magnets pushing it away, I've found you need REALLY strong B Fields to do this. In other words, are we sure this is an effect that is at play here? (I'm asking)