I believe the enamel can be repaired by painting in the parts that are missing. You would probably have to apply several layers of paint, with each layer drying as you go. The paint would have to be built up higher than the edges of the swastika, then carefully sanded back down with a finely grained sandpaper, being careful not to damage the raised metal edges of the swastika. A polishing of the paint might then be in order.
