It sounds like the motor, lets hope not because they are expensive. The motor is a brush type and when the brushes ware they put off dust and they get into the armature and short out . These motors don't have any vent holes and there is no escape for the dust, With other motors of f this type i have taken them apart and cleaned the armature slots with a file being careful not to short out the windings. I have had mine for 3 years and had to replace the motor,
IKE