I could be wrong, but I believe it's Radium burn. From what I've been told from my watchmaker Radium burn usually happens on dark grey dials (which this originally was). If you look around the outer edge of the dial you'll see the original grey. Also in the past when I've seen water damage it usually starts to show on the edge of the dial and not the middle. Here is what the original dial would have looked like. Here is mine now
Hello, greeting from Indonesia. Just get my first Omega last month. Really fall in love with this vintage piece