usually the switching gear of the "E" unit a tooth breaks off of the gear and the gear wont move anymore so it stays in the last position it was left in probably neutral or the fingers below the E unit break off so the field or armature no longer make contact with the gear and the electrical fingers are replaceable . they can be purchased form Lionel parts places on the internet! shame you didn't go to York TCA train meet October 21 22 23 !
post war lionel e unit parts - Bing images
Lionel Three Position E-Unit Contacts and Drum Repair Kit - www.rudystoys.com
Alan