Ok, this is difficult to do without sounding dumb.
I fixed the issue. It was easy, as soon as I took everything apart and put it all back together. The screw on top of the coupler had worked loose. If it’s a little loose the coupler will stop self-centering one way. A little more loose and it stops centering altogether. If VERY loose the coupler begins to tilt.
The loose screw comes from the train going through curves. The swing of the coupler CAN loosen the screw.
After you remove the shell from the frame, remove the trucks. Tighten the screw on top of the coupler. Put it back together.
I mentioned that these were used when I bought them and who knows how many curves they have been through. If this problem ever comes up again, I’ll use thread locker or nail polish to prevent the screw from turning on its own.
Hope this helps somebody. If it ever helps someone, tell me so I don’t feel so dumb.
Thanks MTH, for making a good product.
