The step I forgot to include is to remove the rag stuffed down the duct. The rag is there to catch the dropped screw. If the rag is there, you will NOT drop a screw -- but try it without the rag, and you'll drop 20 screws.

Also, if you have a bad segment in the resistor, you can repair them by soldering a comparable resistor (both resistance and Wattage) on the outside lugs. It works -- I've done several this way, and they're still running.