I also have cracks at all four corners on my '05 FR unit. Each of these extend away from the opening for the slide and are all at approximately 45 degrees. My unit has the Lippert "under sofa" type of slide drive mechanism and I personally think it has to be the worst designed drive unit I have ever seen. ALL of the weight of the slide rest on two (2) rollers attached to the exterior siding of the camper. When the slide is being moved "OUT" the area of the exterior wall below the slide bulges out quite a bit. When moving the slide back in the exterior wall bends back toward the camper. An extremely poor design IMO. From research in the net there is practically nothing that can be done about these cracks as far as a permanent repair. Many will recommend drilling a small hole at the end of the crack to prevent the crack from extending further. My experience with sheet metal has shown that this method does not always work. I've seen new cracks start out from the drilled hole area. My concern has been if rain water could infiltrate into the two cracks at the top of the slide area. For now I have a type of industrial tape over the cracks to help prevent water intrusion. I have an older friend of mine who did custom kitchen/bath cabinets for years and he has suggested custom cutting some Formica countertop material to go over these cracked areas. The camper siding is practically what Formica is, just a "plastic" laminate. He used some type of hot glue in his work to glue Formica onto counter-tops and this just might add some structural integrity to this siding.