UP M-10,000 mod.
Running this train, the ends of each car would swivel on either side of the track, especially in reverse.
The 'couplers' swivel on the large shouldered screw so any side force moves the car to the side. A kadee red insulation washer 'did the trick' and it took up the space on the shoulder so the only pivot point is on the pin (the way it should be).
A good article on weathering in OGR's magazine for Oct/Nov 2020 on page 21.