If you are going to replace the corners...I assume that is where it is rotted...I would highly recommend trying to get the whole top rail from A-pillar to A-pillar. Take it apart at the factory seams. It will save you from getting into allignment issues later. Trust me, I have been there. Post up some pics so we can see where yours has problems. It will also help the seller to know where to cut. Here is what I mean by taking it apart at the factory seams.