Realized that the original bad encoder (#1) probably has a working LED, while the encoder I broke (#2) has everything but a working LED. Thought maybe I could move all the working components from #2 to the case of #1. Started by removing the retaining ring on #1, then pounding the shaft out of the bearings. Managed to remove the shaft, then the two ball bearings supporting the shaft. At this point, realized there was no way we could get the shaft with the glass encoder disk out of #2 and into #1 without destroying the glass, which is very thin.
Ordered several different infrared LEDs from Digikey for about $5. Hoping one of them will work with the broken encoder. Not sure if the light needs to go through the lens or if the LED can be close to the sensor. This is a last ditch effort, but I really can’t lose for just $5.