Speedmaster Professional Day-Date, 
Omega Cal. 1151 (based on Valjoux 7751)

Not so easy to take off that snap-on case back
I used my trusted Bergeon snap-on case opener and when it did not budge at all went to search the internet to find out, whether this was really a snap-on case back. The lack of notches and the perfect alignment of the case back suggest it was. Once I was sure it must be a snap-on case back, I started prying a bit harder and in due course left a tiny ding on the side of the case at the lug at 7 o'clock.
I was able to "press" it back in with the rounded steel bar of the Bergeon opener. Then took the last ridge off with a waterstone and finally sanded the small area with a sanding rubber and I am very happy with that outcome. Would have been really too bad if my curiosity and the hard sitting case back left a visible mark on the side of the case.
Why did I open this Omega purchased in a shopping mall outside Los Angeles in 1997? Because I had noticed that the winding became a bit stiff. So I wanted to see whether there was any visible indication that the movement needed a COA. I could not find any such hint when looking at the movement. I used bit of Moebius Synt-A-Lube 9010/2 for all visible jewels and for the winding wheel. That obviously did the trick. I have now a tiny ding on the side of the case, but also a watch that winds without ripping the skin of the finger cups. So I am definitely happier now. And as always, movement pictures are an additional added value to watch work.