The mistake should be corrected if one thinks that it would improve the translation. It does not even have to be a mistake; the translator can do as he or she pleases, as long as they can offer a good explanation for what they're doing.
Since I don't know much about translation errors of The Three Musketeers, I give you a different example: that of Homer's Odyssey. The first popular English translations used romanized names like "Ulysses" and "Jupiter". This was not a mistake - at the time these translations were made, none of the readers would have known the Greek names, whereas there had been some contemporary works that had popularized the Roman names. Nowadays, the general knowledge of ancient Greece has expanded and it has become more popular to use the actual Greek names. Samuel Butler, who wrote the translation that is available on Project Guttenberg, actually wrote in his preface about his decisions in this regard and said something like "maybe one day, hopefully, the Greek names will be more well-known than the Latin ones".
He also wrote about some difficulties that exist with the Greek names, however. He mentions that there are different cases in ancient Greek that change the name depending on how it is used. He notes that there actually isn't "one correct translation" for Odysseus, and that "Odysseus" itself is some kind of compromise that is only used because it is popular, not necessarily because it is correct. I can say that after reading that preface, I was a lot more content with reading all those romanized names.
There is also a new translation of the Odyssey by Emily Wilson. It was only recently released and is a very interesting take on the epic poem. It tries to re-introduce the meter that was originally used by Homer while also realizing that this meter straight-up doesn't work in English because of the way most words are pronounced and emphasized in English. So the result was to use a different meter, which has one syllable less per verse (or something to that extent). But since ancient Greek is a much shorter language than English, it was not possible to make a nice "poetic" translation anymore with the meter restriction. Wilson instead made the poem unbelievably short and on-point, which increases the pace of the poem and makes it less grandiloquent.
Also, interestingly, she now translates what used to be translated to "servants" and "maids" simply to "slaves". She made a point of doing that because she wanted no sugar-coating of a problematic aspect of the poem. (And those women are definitely slaves. Odysseus kills them later because they had been raped.)
I'm telling you all of this because it shows how many different problems there can be when translating literature. It's not simply a choice of replacing one word with another. Sometimes, a translator may deliberately choose an incorrect translation because he knows it will help the reader, as was the case with Samuel Butler's translation. Emily Wilson instead chose to be radical because she wanted something that had been lost in translation - the original meter, which itself needed to be "translated" into English. And she wanted a modern translation that fits our times better than those of translators who still might have been slave owners themselves. Yes, there was some backlash against her translation, and I am also not happy with some of her choices. But it adds something that the other translations are lacking, and for this reason alone it is good that it exists.
Nobody starts a new translation because they want to keep everything the way it was. And nobody reads a new translation and expects a replica of the old one.
If you are actually translating The Three Musketeers at the moment, my suggestion is: change "studs" to "aglets" and make a footnote detailing what aglets are, and how they were used. Personally I love learning something new in my novels.
