I wouldn't worry about the gasket. A used watch generally needs a servicing, and the gasket gets replaced during a servicing.
That said, your pics are awfully blurry, but might be good enough. I'm not an expert, but I do have a copy of the Moonwatch Only book:
Dial appears to be the type used from 1997 to the persent day (luminova, not tritium)
Bezel appears to be the type used between 1995-2004.
Movement appears to an 18-jewel yellow-gilded 861, from 1995-1997.
Caseback appears to be the modern type (1995-present day), but the blurry pic makes it hard to be sure.
Inside caseback shot is unreadable.
From the "840" on the endlink, I assume the bracelet is a 1998/840 (this should be on the inside clasp), from 1999-2002.
One issue is that your case has no serial number, unless it's been photoshopped out. There should be one, and it should match the one on the movement (which we can't read in your pics). It's possible that the case was replaced due to damage, though.
Another unknown is that, while the following is suspected to be true, we don't have any evidence for this movement/dial combo to have been used together. Given Omega's practices, it's quite possible. However, this combo is more likely to occur because someone had the dial (and maybe the hands) replaced because of non-functional lume.
The newer bracelet could be because a previous owner liked the newer bracelet more, or because the original bracelet was damaged along with the case.