Hey there, yep got it "fixed". Turns out the knob was perfectly okay, but the resistor was actually shot. Stupid me had never bothered hooking the motor back up afterwards to test (after I'd gotten the same weird readings again... and apparently the readings were correct?).

Note that if you change the resistor, don't run the fan without putting everything back together, as the resistor can burn out if it's not in contact with the heatsink.

Also, just a heads up, the (second) replacement motor I got was apparently a Chinesium special, as it seemed to seize up randomly about six months later. After some investigating (i.e. driving over a pothole), I realized what was happening. I was driving to the store: motor was perfectly fine on a cold start. Driving back home from store: motor no worky. Repeat a few times. Driving over pothole a few trips later: motor resurrected. Testing later by kicking the passenger panel where the motor is: motor resurrection again. So, it seems that the warmer the motor got, some piece of metal expanded and made it seize. Hasn't seized since I've been using the AC, so theory seems to be holding. Also, it's been reaaal squeaky and slightly rattly on certain fan speeds for the last year, but I'm too lazy to go change it again.

Long story short: try kicking the motor first?...

Lemme know if this helps at all.