Does this mean that Lionel is the source for repair parts for Modern Era trains going back to the early '80's? I notice most of the parts vendors carry primarily post-war parts.
No. Lionel sold off their stock of old parts a number of years ago. They clean out old stock parts periodically.
There are many Lionel parts dealers who have a combination of old stock and reproduction parts. Folks will probably post links to their favorite dealers. I use several.
Here are a few:
