Intermittent AC/Heat after FSR replacement

[330Coupe]

After searching forums last spring, I replaced the final stage resistor (with the correct heavy prong part) on my 2003 X5. The fix worked through winter and into this spring. However, I now have every symptom of a failed FSR. Selecting various modes such as AC or Defrost "may" produce results and other times nothing. The rear always works. Temps work fine whenever the unit works. Tore everything apart and made sure the FSR hadn't become loose due to road vibration and put it all back together. Ironically it started working....for about 5 minutes. The plenum doors can be heard activating with each selection, so I suspect it isn't a bad AC unit. Sounds like the replacement FSR has gone bad. Could this be the result of an inferior knock-off part manufactured by one of the parts warehouses?