if it's any consolation, similar problem on the oem hydraulic rollers in the newer HEMI's. it's not that frequent, but it's not unheard of either. There appears to be no rhyme or reason to it. Near as anybody can figure it is the outlier defective part. It can happen on an engine with only 10 or 20k miles, or one with 60k. You just hope it's on warranty.