Reply to "Lionel 623 Switcher Problem"

So based on your comments, I started to think about what could be causing the short between segments A-B. The first thing I thought about was the slot between A-B. I always clean the slots between the segments whenever I service any of my engines, but this time I really cleaned out the slot between A-B. Then checked the resistance between the segments again and found that the resistance between segments A-B now shows a reading of ~1 ohm, similar to segments A-C and B-C (refer to attached video). I placed the locomotive on my test track and it ran.  I oiled the thrust bearings on the armature shaft and placed the locomotive on my platform. Now it runs great (refer to attached video). I never realized how important it was to keep the slots between the segments clean in order to maintain a smooth running locomotive. Thanks to Dan, Ed Horan, Rob and David Johnston for your extremely helpful comments.