> The one electrolyte capacitor on all of the three motors look O.K
> from from the outside. What could it be most likely that makes 
> 3 out of 6 motors fail so completely?

Be very wary of electrolytics over around 20 years of age.
They can go dry, short, even explode (I had one go off like a
hand grenade in a Korean War vintage shipboard transmitter that
I used to run in my ham station... it tore up the modulator and
RF decks, rather significantly).  Computer grade caps are usually
high quality, but, can go dry with age, if they have been run hard.
Blowers are generally run pretty hard.  I am not sure of the exact
circuitry in your blowers, but if there are sillycon bits and 
electrolytics present, it probably is a dc-ac converter driven
AC motor.  Theoretically they are good, but practically the
electronics bits can go bellyup.  IFF you could sub a traditional
AC motor directly, e.g., an air conditioner blower motor or such,
you might be better off.  Just thinking out loud....

Bob