I would have to agree with the flex shaft choice as well. I recently
had to replace a Foredom S unit, however, it had given up after 22
years of nearly daily use. A couple changes of brushes, a cable and
sheath or two, regular shaft lubrication were all that it needed in
all those years of power brown outs and demanding use. Due to
assuming it could be repaired, I sent it off and was thus unable to
give it the burial it richly deserved.... It's foot pedal lives on...