Old thread, but had similar problem with my Dart. When through atleast 3 regulators before finding a VERY intermittent short in the field of the alternator. Ohmed out the field and slowly turned the pulley. Every once in a while it showed shorted, but wasnt like every revolution in the same spot. Brushes looked fine.
That’s good info right there. Sometimes these anomaly’s can’t be detected and we just end up throwing money at it without really knowing or figuring out what the real problem is. Thanks.