DC05 turbo pet hair brush

The inner rotating brush stop mving when it touchses the carpet. Turning the head upside down and it starts whizzing around again. It seesm pretty weak.

I have taken it apart and cleaned out all the gunk but its still the same. Does the little belt need replaing in the head or something else?

The dyson has plenty of vacuum and the other heads are fine.

I have two pet hair (turbo brushes) that have the same fault.

Thanks for any help!