[JesseK]

When I first put the gearbox and FP together a few years ago, I spun the output shaft with my fingers to double check that things were together properly. It turns out that I didn't have one of the 3 bolts fully tightened, by roughly 1/4-turn. After I took it apart for inspection, re-assembled, and tightened it down again things spun smoothly. We used Loctite after that.

Given that the teeth are 32DP (i.e. very small), there's very little room for misalignment. Double check that things are still tight. Also double check that there aren't any imperfections (chips, dings, dents, etc) on the gear teeth themselves, as that would also cause seizing (maybe the motor with attached pinion gear moved around in a loose box in the car on the way home from kickoff? It's happened to us).