This being a brushed DC motor, most heating is prolly coming from the
rotor coils. Or is it ?
Could there be eddie/induction currents that are heating up the
exterior ?

When I do heavy milling that this motor/mill was never designed
for , the exterior gets hot to the touch.

If the heat is coming squarely from the rotor, via the 2 bearing and
air gap, the rotor itself must be mighty hot !

I am thinking about getting some compressed air to enter the motor's
interior - somewhere near the brushes, go up through the gap stator-
rotor gap and then out (will prolly require a hole or two on top).