If the brushes no longer work, it is possible that the problem is caused by the failure of the MOSFET that is responsible for powering the motorized accessories. This vacuum cleaner model (Dyson V8) contains a MOSFET M13C30/ PSMN013-30MLC (N-channel 30 V 13.6 mΩ logic level MOSFET).
In this case, replacing this MOSFET solved the problem.