I would get a new retaining ring, just in case. It may have been in place 40 years, and could be a real pig to get out. On the other hand, it may come out undamaged, but better to have a spare in case you end up breaking it up to get it out, at least you can finish the job that way! And if you don't need it, you can always keep it as a spare or sell it on. Don't forget to drill out the staking before attempting to remove the old one, and good luck with it.
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