Allow me first to clear the smoke for you. In any major city there are usually multiple Rabbis who may indeed provide you with different answers to the same question. What to do?
First of all Jewish Law does not allow you to shop for a Rabbi who's ruling appeals to what you are seeking. One is supposed to have one Rabbi and to follow his rulings. Otherwise you turn Judaism into a "supermarket shopping" experience.
Now if you ask many Rabbis about the sequence of events that are written to occur prior to the revelation of Moshiach [Judaism's King Messiah] the vast majority will tell you about the Prophet Elijah who supposedly comes first to announce Moshiach's arrival.
Such opinions are based upon what Torah states. These opinions are valid... therefore...under but one possible scenario for Moshiach's arrival.
However when it comes to determining who has the final word on this disputed topic one need look no further than Maimonides' Laws of the Foundations of Torah. This legal work states that a Proven (demonstrably proven to be true) Prophet must be believed and obeyed.
Rabbi Schneerson enjoys the status of being a Proven Prophet. As Prophet his grasp of Torah trumps all other Torah Sages.
Now...regarding Elijah's arrival and the sequence of Messianic Era events....please read the following which is based upon the Teachings of Rabbi Schneerson.
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There is a tradition that Eliyahu (Elijah the Prophet) will come before Moshiach, to inform the world of the advent of Moshiach. Is this showing of Eliyahu a mandatory pre-requisite for Moshiach?
The Talmud relates:[71]
Once, Rabbi Joshua met Moshiach and asked him: `When are you going to come?' Moshiach replied: `Today!'
Rabbi Joshua then met Eliyahu, who asked him: `What did he (Moshiach) tell you?' Said Rabbi Joshua: `He lied to me, for he told me that he is coming today, but he didn't come!'
Said Eliyahu: `He didn't lie, but this is what he really meant: He will come "Today, if you hearken to the voice of G-d."[72]
Maharsha explains that if Moshiach comes today, we assume that Eliyahu came yesterday to the Supreme Beth Din (in Tiberias).
Another explanation is that if we merit, and Moshiach comes sooner (before the appointed time), he may then come on his own before the revelation of Eliyahu. This is presented in Krayti U'playti (by Rabbi Yonason Eibschutz):[73]
Rambam posits[74] that it is not a certainty that Eliyahu must come before Moshiach. Although some Sages maintain that before the advent of Moshiach, Eliyahu will appear, yet, there is no definite basis for this.
This poses a difficulty, inasmuch as the Talmud states[75] that Eliyahu will come first, and as is seen in Tanach,[76] "Behold I send unto you Eliyahu the Prophet." How do we reconcile these two statements re: the coming of Eliyahu?
The answer is seen in the timing of Moshiach, as the Talmud cites the verse:[77] "In its time will I hasten it" - If Jews do not merit, Moshiach will come in his appointed time; but if they merit, then Moshiach will come sooner, in haste.
Rambam holds that there is an order to the coming of Moshiach, that Eliyahu comes first to foretell of his coming. This, however, is effective only when Moshiach comes in his appointed time. But when Jews merit and the redemption is hastened, as expressed in,[78] "He is leaping over the mountains, skipping over the hills" - G-d then changes the order, as a sign of His love for Jewish merits and good deeds. This is expressed in the Rambam's concise words.
The Sages note that Eliyahu comes first, to convey the news of Moshiach; yet, this is not definite. For, perhaps G-d will have mercy and bestow His holy spirit upon the Jews to serve Him with a full heart; then He will swiftly bring Moshiach without the need for Eliyahu's message.[79]
Notes:
71) Sanhedrin 98a, Rashi
72) Psalms 95:7
73) Yoreh Deah 110, Bais Hasafek/end
74) Hilchos Melachim 12:2
75) Eiruvin 43b
76) Malachi 3:23
77) Isaiah 60:22; Sanhedrin 98a
78) Song of Songs 2:8
79 )Otzar Blum, Sanhedrin ibid.
[my thanks to Rabbi Abraham Stone for compiling the above from Talmudic, Midrashic and classical Rabbinic sources.
- Rabbi Moshe Yess]
