Just been attempting the same task in order to service the motor.It is quite difficult without a repair manual but basically proceed as follows
Remove the sole plate covering the brush and belt drive (4 screws).Disconnect the belt and remove the brush. The beating head must now be removed. This is quite tricky. On the side opposite the belt drive the head is attached to the main body with a plastic plug which is anchored to the body with a slotted flange fitting into a plastic projection. This can be eased off and the plug removed. On the belt drive side the problem is more obscure as the foot pedal and flange have to be removed carefully (3 screws) allowing the flange to be disconnected from the main body. Take careful note of the way the foot pedal mechanism is fitted.
This now allows you to access the motor housing which can be opened by removing four screws. Make sure the unit is unplugged from the mains and remove the two connectors on each side of the motor which can now be lifted out for cleaning and access to the brushes. I am not sure whether replacement brushes are still available.
ouchie
December 2009