What exactly did your dealer do to correct the issue? Did they replace the tailgate or just grind or bend the part back to a round shape?
My 2016 2500 has had this issue since new. They've probably replaced it half a dozen times if not more. Last time they replaced the cup that bolts to the truck side that the tailgate sits in along with the bushing. This replacement lasted the longest but not much more than a few weeks or so.