Mike, Since you said you also had this magenta cast you had not been able to get rid of, do you have a way to try the steps I try at your own scale. Is that possible for you ? I am not a chemist or far from me, but I came up with those steps after imagining a way to reduce developer activity... and it worked. In fact if I kept reducing the temperature and agitation, it starting showing a slight cast in the opposite direction.

Pentaxuser. the clue that I had was; the publication states:

"Processing conditions may affect the color (hue) ofPORTRA Black & White Paper. You may see a hue change on the magenta/green axis due to variations in developer tank activity and pH. Low developer activity and/or pH (typicallysevere oxidation and/or under-replenishment) will cause ashift toward a green hue. High developer activity and/or pH(usually over-replenishment) will cause a shift toward a magenta hue."

Tell me if my reasoning makes sense, or just a very lucky shot...
thx