What I have been doing, is roughing up the surface, and using a black body panel adhesive type cement to hold them together and coat the whole surface. I have even been doing this on good panels, as it prevents them from cracking.
These strips are PATHETIC. There is a thin metal core, and then they are extruded. unfortunately, the core only runs on the top! If they used a T-channel type core, these things wouldnt be falling apart. They crack and fall apart very easily once they are brittle... just by catching the edge with clothing you can break them... nevermind getting a door panel apart.
I have considered making machined aluminum replacement pieces, but it would be extremely cost prohibitive to do so unfortunately.