still i will open the 1 that has been installed just to learn the condition of the brushes. if worn out will replace them (or the voltage regulator that comes with them). i guess that was the reason for the erratic behavior.
and when i install the new 1 will check its performance and tell here.
but may take some time, as the symptoms have been erratic.
once again, thanks a zillion for all the terrific help.