Replaced the capacitor today and it fixed the problem.
The old capacitor looked fine physically- there was no bulging or anything of the sort, nothing about the appearance would have led me to believe it's bad. But I got no capacitance reading on the HERM side, and the fan side was reading 2.5uf instead of 5.
My cheap E-bay meter must be halfway accurate because the new one tested right at 45/5 uF within a tenth or two.
Capacitor cost $24 at Winair, I guess if something on the AC were to fail, that's the one you want it to be! Thanks to all for the help/suggestions.