When I took out the motherboard from the iphone4 this little rubber spacer with a little slit in it fell off. I can't find any info of where this piece goes This was located near the top with all the clips of the iphone4
The rubber piece fits on top of the motherboard where the two screen ribbon cables bend over the top of the motherboard. This is a bumper to protect the ribbon cables. This area is to the left of the area where the top-most screw goes.