Being new to this O gauge world, I am very very surprised at the apparent reluctance of folks to send cars with defective couplers directly back to Lionel, demanding repair, replacement or refund. You paid alot of money for these cars and they should work right out of the box.
In my prior hobby of 50 years (firearms), if anybody buys any type of new firearm that does not work due to a manufacturing or design defect, they have no hesitation in boxing it up and sending it straight back to the manufacturer for repair, replacement or refund. They don't stand around discussing it. In most of the cases, the manufacturer promptly takes care of the problem and sends it back.
Why the reluctance to send these back? If Lionel comes up with replacement trucks or couplers, why should YOU have to replace and install them. Make Lionel do it.