It's not so much a defect as it is (from what I've seen) a function of who owned the car and how it was treated. I've owned, drove, and repaired or parted out a couple hundred of these cars over the years and seen that issue regularly.
Also, I've been fortunate to be around some cars that had the same owner since new.
What I've NOTICED (which is to say not read about or seen documented) is that it happens more frequently in cars people pushed themselves upwards by resting a hand on the door top or armrest when entering and exiting. Heavy door with added weight from the person leaning, metal fatiguing etc.
I have not noticed a correlation to mileage, trim level, or options. Equal frequency for base vs limited/brougham, pw/Pl vs manual, etc. Even had a 34k original mile base trim car crank window car with that issue. No issues with door dines or worn striker pins making contact when closing on most of the cars either.
As far as repair, you'd really want to weld it and make sure nobody leaned on the car getting in and out. Plastic is likely to crack due to how heavy these are and wouldn't look right by the time it was built up thick enough.
