Hi Omega78, are they photos of the same watch?
From what I've read, mark 4 and mark 4.5 should have this yellow seal between the mineral glass and the bezel.
Please check out Chuck Maddox's brilliant website -
http://chronomaddox.com/c1045_in_detail.html,
To see some excellent examples, some of which have just been refurbished by Omega HQ
My Mk 4.5 certainly does - But I can't say that I actually like this feature, on an otherwise fantastic watch (especially for the money, as these can be picked up relatively cheaply)
Cheers, Paul
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