New gaskets, new crown, new crystal, maybe new tube if it is worn and you should be good to go up to 3-4bars probably. The difficulty would be locating identical crowns and crystals (some are specific, with sandblasted finish for example), but generics could do the job.
FWIW, a 1950s Seamaster (not even a screwed back) can withstand a few bars (with new gaskets, crown, etc). You will have to check it very regularly, it is never eternally water resistant and the world is full of water damaged divers.
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