The motor seemed to be fine but "lazy" due to a poor battery.
I've always had the idea to try to repair "things" before I throw it away. It is more or less a challege I've given myself. This was also the case this time :)
I used a big flatheaded screwdriver to turn the bottom of the thootbrush 45 degrees counterclockwise.
Push the motor/battery assembly out like its shown on the photo (red arrow).
Unsolder four points. 3 x for the motor (green circle) and 2 x for the battery (red circle).
Lift the pcb away and pull or lift the battery out of the plastic holder. Notice where the thin wires from the charing coil is running!
The order of the bottom assembly is coil spring, chipboard washer, coil, rubber washer, plastic cover
The battery I used is a Sanyo 14x50 mm. 1,2V NiMH, 1500 mAh rechachable.
Notice that the + on the battery should be towards the motor. Use a multimeter to find +/- on the battery.
Put the battery in place and solder the motor and the battery to the pcb. Make sure the thin wires from the coil is ok.