You are probably in the minority who think it is a design or assembly defect. So it is just as well you do not get one, obviously it is not for you which is why there are 50 DLSR cameras out there, someone thinks at least one is just right for them. Of course only one of them has IQ as good as the D600.
But you will notice on the internet, every one of those models has some group of people screaming about real or imagined problems even if they never shot with one before. That is the nature of the anonymous internet. You will notice that those who complain the loudest tend not to use for taking photos and prefer spending much more time writing about how terrible it is than it would take to clean off a little dust. That to me is what is astonishing. But then, I once had a GF who insisted she needed me to get her a new 450SL because the old one was dirty. She soon became ex-GF. The main difference is cleaning a sensor takes 3 minutes and detailing a car take 8 hours, and paint is much more fragile and expensive to repair than a tough AA filter. Stan St Petersburg Russia