Eliyahu HaNavi's role in Moshiach's arrival according to the Rambam

Question

The Rambam says in Hilchos Malachim 12:2:

There are some Sages who say that Elijah's coming will precede the coming of the Mashiach. All these and similar matters cannot be definitely known by man until they occur for these matters are undefined in the prophets' words and even the wise men have no established tradition regarding these matters except their own interpretation of the verses. Therefore, there is a controversy among them regarding these matters.

_{Translation from Chabad.org}

Two related questions:

1) Where is Eliyahu's arrival debated that you could describe it as "some Sages" and "controversy"? Presumably the Rambam learns from the Bar Kochba events, where Eliyahu Hanavi didn't make an appearance that it is, in fact, uncertain when in the process he will arrive, but is this actually explicitly argued anywhere?

2) In Hilchos Nazir 4:11 the Rambam says that someone who vows that he will be a Nazir on the day "The son of Dovid comes on" is a Nazir from that day forward, unless he makes the vow on Shabbos or Yom Tov. Because there is a Safek if Moshiach can come on those days, his vow only starts the day after (but is effective even on Shabbos and Yom Tov subsequently). What is the doubt about Shabbos and Yom Tov? The Kesef Mishna, the Midgal Oz, the Radbaz, etc. all point to the doubt about whether or not there is "Techumin" above. If there is, then Eliyahu HaNavi can't come on Shabbos and Yom Tov, so Moshiach can't come that day.

So from this we see clearly that Eliyahu HaNavi is an integral part of Moshaich's arrival and not subject a matter for which there is no clear tradition.

So which is it? How exactly does the Rambam understand Eliyahu HaNavi's timing in the arrival of Moshiach?

Answer 1

One source is:

Yerushalmi Eruvin 34b

שָׁאנֵי הָתָם, דְּאָמַר קְרָא: ״הִנֵּה אָנֹכִי שֹׁלֵחַ לָכֶם אֵת אֵלִיָּה הַנָּבִיא וְגוֹ׳״, וְהָא לָא אֲתָא אֵלִיָּהוּ מֵאֶתְמוֹל. The Gemara answers: It is different there, as the verse stated: “Behold I will send you Elijah the prophet, before the coming of the great and dreadful day of the Lord; and he shall turn the heart of the fathers to the children, and the heart of the children to their fathers” (Malachi 3:23–24). This verse teaches that Elijah will arrive the day before the coming of the Messiah. Since Elijah did not come the previous day, the Messiah will not come today, and therefore he may drink.

Rabbi Michael J. Broyde:

My own intuition is that Rambam used logical tools to resolve disputes and was not even fully wedded to the notion of the complete superiority of the Bavli over the Yerushalmi in all cases.[2] That Rambam does not follow normal rules of decision is widely noted. (See Sedei Chemed, Kelalei ha-Poskim vol. 9, siman 5. See also numerous such references in the Tosafot Yom Tov; Rashba, Ketubot 48a, s.v. amar Rav; idem, Nedarim 46a, s.v. mistavra; Ritva, Moed Katan 8b, s.v. ika beinaihu; Yam Shel Shlomo, Yevamot 8:18; Penei Yehoshua, Gittin 84b, s.v. ve-nir’eh le-Ri; Chatam Sofer, Avodah Zarah 34a, s.v. ve-ana kevedah [perhaps].) The more I immerse myself in the study of Talmud, the more I understand the reference to the “sea of the talmud.” It is not called a “sea of Talmud” because (as some have joked) it is so easy to drown in it. Rather it is because no matter how much time you spend in it, it is so hard to understand its many currents, ebbs and flows. Just when you think you understand how the sea works, you learn something new about it.