Thanks everyone for the tips,it will be Sunday before I can take apart. It looks like two brush holders on this model,still not sure what the slip ring is,guessing where the brushes ride? If so that area looks dark and dirty. What is the best way to measure the ohms,should I take 0-4 off regulator and turn motor over?
Check field boost on wires 0 and 4 from the PCB ?? Does this mean right at the brushes,if so very easy to get at. This unit the whole side panel comes off for easy access.
Unplug 0 & 4 from the PCB board going to the AVR. If that unit has an all in one plug on the AVR just unplug it there and read the field boost. I think you may have answered the question now that you said you see the slip rings and they look dirty. I bought a commutator stone from Grainger supply 8 years ago and am still using the same one to polish rings!