Spetacular piece. I am lucky to own one too. Loooooong search and research. My sources let me to conclude 7 pieces in existance, but at the end, only PP knows.
I love the 2499, 5004, 3970, 5970. However, the 3970 was the first I purchsed and has always been special to me. Love the pump pushers and the simplicity. I like the vintage look and feel, and the size is just perfect for a dressier watch.