THE BUCKLE ON THE SEAT FAILS TO STAY BUCKLED. MY SON WAS RIDING IN THE SEAT REAR FACING WHEN I HIT THE BRAKES GOING 35MPH TO AVOID A COLLISION. THE NEXT THING I KNOW MY SON IS SCREAMING MY HEAD HURTS MY HEAD HURTS. SO I PULL INTO THE NEAREST DRIVEWAY TO FIND OUT WHY HE IS CRYING ONLY TO FIND HIM WITH THE BOTTOM BUCKLE UNBUCKLED (WHICH HE IS PHYSICALLY INCAPABLE OF UNDOING HIMSELF) WITH HIS BUTT WHERE HIS FEET SHOULD HAVE BEEN AND HIS HEAD WHERE HIS BUTT SHOULD BE. THE CHEST CLIP STAYED BUCKLED AND WAS THE ONLY THING KEEPING HIM IN THAT SEAT. EXCEPT FOR IT WAS LODGED IN HIS THROAT. HE WAS ESSENTIALLY HANGING FROM THE CHEST CLIP AND HARNESS BEING STRANGLED BY IT. SO I RE-BUCKLED HIM AFTER CALMING HIM DOWN AND DROVE HIM TO THE NEAREST ER. AFTER WE LEFT THERE I PUT HIM BACK IN THE SEAT AND PULLED ON THE BUCKLE AFTER HEARING IT CLICK TO ENSURE IT WAS BUCKLED, TO ONLY HAVE IT SLIDE OUT ON IT'S OWN UNDER MILD FORCE. SO I PUT HIM IN HIS BROTHER'S SEAT FOR THE RIDE HOME SINCE HIS BROTHER WAS NOT WITH US. HE HAD BRUISING AND SWELLING INTERNALLY AND EXTERNALLY ON HIS NECK, BUT LUCKILY NOTHING ELSE. YES THE SEAT WAS INSTALLED CORRECTLY AND BUCKLED AND TIGHTENED CORRECTLY WHEN THIS HAPPENED. I AM A CPST, SO I KNOW IT WAS A SEAT FAILURE NOT A USER ERROR. IT IS MODEL OF BRITAX MARATHON 70 E9BB11Q SINCE I COULD FIND IT IN THE MODEL LISTING. *TR