Buy it, send it to Omega for a service and it will come back looking like new with many years of enjoyment to come.
And no worries of caliber 2500 problems. But don't get keyed up on that stuff anyways. Yes Omega has 3 revisions after the original 2500 to correct some issues but even if you bought one of the pre D model watches, Omega has a few things they do differently now during servicing of the A B & C to help prevent the original issues and they run ok. Every mechanical watches requires servicing and I personally do it to any preowned watch I buy if I don't know the service history no matter how well its running.
1120 is in my opinion tried and true, 2254.50 is a great place to start.
During service, note anything thst concerns you such as the clasp and they will fix it. Its either the diver entension needs to be peined (tightened) and clasp spring replaced. I don't see any issues in terms of stretch. Get Omega to check the pins and tubes for wear. (Loose pins)
BTW, the bezel is in good shape for the condition of the rest of the watch. This seems to be one of the more common parts that becomes scratched.