I found the review by ronstowe to be very informative and accurate.

I would like to add an additional caution. I recently purchased a model 30 mixer which had one of the black plastic brush cap broken off exposing the brass screw underneath. I plugged it in and gave it a try. It was not running but I put my hand on the motor and barely contacted the exposed brass piece and  I got a small but memorable jolt.

I  repaired it and wondered what would have happened if my other hand was well grounded???

I followed ronstowe's advice and rewired the mixer adding a ground wire (3 prong) plug. It may not look original but it's safer.