The couplers on the American Models cars are made from Delrin.
As Francine has said, the problem is the talgo arm that connects to the trucks. It seems hit-and-miss whether the arm is warped or not. Even the scale cars (at least the early ones) had some warped talgo arms, I wound up replacing them with body-mounted Kadees on my scale heavyweights.
I think if I were to try and correct the talgo arm, I would cut off the arm leaving about 3/8" on the coupler. Replace the arm with a piece of brass stock or Evergreen channel and screw the coupler to the new arm. It would be a trial and error project on the first ones.
Rusty
