I replaced the gasket on a GW-530, and now there appears to be a slight gap between the caseback and the watch. That may not be the sealing edge though, I have no idea. I did open it up after running water over it, no water inside like there was with the faulty gasket.
Is a tiny gap anything to worry about? I have a feeling that isn't the sealing edge. The watch held up perfectly to being submerged in water 2 inches deep for an hour, but that isn't much of a test. It does fog up on the inside in the cold, but the same happens to my never opened GDF-100