Can you draw the circuit? A photo of the board and the mixer internals would help. Rufus's suggestion of a diac is a good one, but that would mean there has to be a triac or thyristor.
I was thinking it may be a spark gap surge arrestor which may be directly across the motor. If it is, it will look like an open circuit, and it will be fine as long as the glass is not broken, and it can go either way - it would not be polarized.
I assume the mixer somehow can vary the motor speed. It could use different resistors, or capacitors to affect the speed, or it could be there is more circuitry you cannot see - perhaps built into the actual speed control switch or knob.
Also, how has it failed?
Richard