responded to my email
Over the next couple of days we exchanged information describing the normal use, loads etc.
If the climate is warm you should be holding the Preheat/Bypass switch for about 10 seconds before cranking and an additional 5 seconds or until the oil
pressure has come up after starting.
Load the unit very heavily almost over load it if possible only for a very short time.
By doing this you will put very high voltage to the exciter field and hopefully raise the residual magnetism of the Rotor. This magnetism is what gets the voltage going upon start up of the unit, if it is low it may sometimes not get the AC Regulator
When shutting down remove all
load, let the motor run for a few minutes and then turn off.
It has worked well so far, spare set of brushes are on order.
Many thanks to NL for their advice