I got one of these recently, and the crystal didn't just crack, it exploded. I didn't even bump it on anything. I was walking into work, I hear a loud pop, look down, at there are bits of glass on the floor and my watch has a jagged edge where the crystal once was.
I cut the bottom off of a paper cup, and taped it so that it protected the dial until I could get it home. I took the watch apart, removed the rest of the glass, and measured the opening, its about 37mm. I had a sterkreuz HH plexi in 37mm from an old project, so I popped that it. Unfortunately, its not quite tight enough to be water proof, so Ive ordered a few more in 37.2mm to try out.
I thought about getting another sapphire or mineral crystal, but I'm not sure how tall the inner dome would need to be. The original crystal is not a conventional shape, and I have never seen one like it sold by any of the parts suppliers I use.
The good thing is that the plexi looks really nice in this watch, and even though its not gen-spec, I think it fits the spirit of the piece more.