The cabs start to rust in this area for a couple of different reasons: The roof skin "flange" is spot welded to the drip rail all along the perimeter. As one knows you cannot weld through an insulator so this is usually bare carbon steel when the welding takes place. This produces a "sandwich" of sheet metal, (one layer on top of the other) and there are inherent voids between the spot welds. This is usually not adequately sealed on the inside of the cab and the condensation of a cold roof panel, coupled with a warm operators cabin produces condensation that accelerates the sheet metal corrosion. The seam sealer that is poured and worked into the gutter is to seal the outer flange area and bury the weld seam. It does nothing to protect from the inside where the corrosion starts. The best way to delay the onset of this degradation, (corrosion) is to seal the inside of the cab. Anything, new or old will benefit from this action. I use a product call "Rust Fire" that sprays on almost like a lubricant and litterally runs into cavities, and then solidifys into a wax effectively sealing the area from moisture intrusion. Although this not absolutely perfect, it works much better than nothing at all to counter the elements. It also smells like asphault for about three solid days so there is a delay to return the vehicle to service. The stuff also stay sticky for that same three days! As was mentioned, one could cut the drip rail off of the cab and fabricate some type of arrangement to retain the roof skin but it would either not look right, or function properly. Although a Mack cab does not gain major strength through the roof skin, there is a lot of vibration present and if not welded solid in some fashion, will crack. I like the four inch wide band type repair myself. I can just imagine how that would look. Rob