I repaired a smelly Kenwood Chef years ago - the main issue was a build up of icing sugar around the commutator and brushes - that, and one of the nylon gears. kenwood customer services were excellent and sent me the gear COD - perhaps they still do this.
If the Triac (switches AC to control motor speed - 3 connections) is defective the motor speed control will not work. If the Capacitor is defective the motor probably won't start. If the resistor is open circuit or all burnt up then replace it. If the motor actually turns over and you can adjust the speed then none of the bits you mentioned is likely to be faulty.
Start by giving it a good clean up and see what happens. The symptom you describe suggests that the motor is running hot and will, if left like this, either burn itself out and/or cause one of the components you mentioned to fail. To replace all three on spec is like changing light bulbs before they fail...
Good Luck
Peccavi
October 2008