After we get information we simulate as same situation that occurred from customer site result fail as well but normally at dock audit inspection & product audit did not check same as customer found (detail in video ataached) and then we consider about phisical characteristic of plate of sleeve and slot of headrest rod and we found when plate sitting in slot , they have torralance about 0.2 mm only and depth 1.6 mm also that make easily to they sitting incompletely if they pulling up faster anyway we was not complacent this problem we will be re-check current part specification and efficientcy of plate sitting situation as well. (detail in attached file)