same here, but not looked in to it yet, pulling down is ok but soon as it goes up it lock into the up part and can not be pulled down again unless fully up
There's a gravity plastic bit inside which stops the belt if the car rolls. This caused a sticking problem on mine. With the seat in the normal upright position undo the screws on the roller thing cover on the back of the seat and have a look inside. If you try to do it with the seat folding forward you will jam it like I did until I realised how it works.