@TheLloyd posted:red from the winding is grounded on the brush plate screw. The other green from the winding remained untouched on the lug between the brush holders.
That is not a ground connection! That is the red field wire strain relief lug and must be insulated from that screw in the same way that the green winding is on the insulated strain relief lug between the brush holders as you have observed. If it is grounded, it will only run in one direction.