It looks a nice solid watch, yes it should have a DON bezel but that’s what happens at official services, key parts are lost for service replacements.
Research well who you want to service this watch, someone with knowledge on vintage expensive watches, any marks on the dial caused by a bad service will hurt the value.
You will also wants to keep the hands in original condition, that spear point chrono hand is worth a pretty penny on its own.
Good luck..
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