[sk8ingdom]

> Improper coating causing a thermal problem, either causing a sensor to fail, lie or some electronic component to break it's solder.

This is the leading theory. Most of the observed failures seem heat related and are likely due to an increased resistance of the brush to shunt connection. This can be caused by quality issues of the brush rivet during initial manufacturing (coil coating) and/or improper torque of the brush shunt screw during assembly (installation error).

The variation in resistance at individual brush sets can lead to uneven current density, causing high heat at the brush to commutator interface which results in excessive wear and damage to the commutator surface and/or brush and ultimately leads to a starter generator failure.

In addition, the software wasn't reporting failure of the component.

I should add a disclaimer that root cause failure investigation is extremely complicated and difficult. It's possible that not all failures were / are the same and there are many other possible contributing causes.