From an Orthodox blogger, first post:
"Let’s face it, in the Orthodox Church, the Masoretes and their Masoretic text of the Hebrew Old Testament have gotten a bad name. It is argued almost universally that Orthodox Christians ought to use the Septuagint Old Testament, because
(1) It represents a translation of an older Hebrew text,
(2) It includes books not found in the Masoretic text,
(3) the Apostles used the Septuagint, and
(4) the Masoretic text is corrupt due to changes that were made in the text in order to obscure Messianic prophecy.
After all, why would you follow a medieval Jewish text when you could follow a Greek text preserved by Christians from the beginning? These are rather strong claims to make, so it is incumbent upon us to investigate if they are true and to what degree they may or may not be accurate. In order to do this, I will write a series of posts investigating these claims in order to paint an accurate picture of what the Masoretic text and the Septuagint really are. This could take some time, so bear with me as I gradually unfold this rather complex issue." [end quote]
The author continues to note:
"There were multiple versions of the Hebrew Bible circulating at the same time. They represent “snapshots” of the various stages of the development of the Hebrew Bible that were taking place even up to the time of Our Lord."
"While the Masoretic text itself represents the culmination of a tradition of textual transmission in the Middle Ages, the text itself is much older, going back to the time of the Second Temple."
"The Masoretic text was meticulously kept, literally down to the letter. Along with the antiquity of the Proto-Masoretic text, it is wrong to claim that the Jews changed the text of their Bible in order to obscure certain Messianic prophecies." from the same section, "...I will demonstrate in a subsequent post, there are instances where the Septuagint itself obscures Messianic prophecy!"
"The preference for the Septuagint in the Orthodox Church cannot be said to be on account of the poor state of the Masoretic text or that the Septuagint is always or even the majority of the time an earlier or more original text. This simply cannot be demonstrated from the facts."
From the author's second blog:
"The LXX/OG never satisfied Palestinian Jews, who were all too aware of its differences in comparison to the Hebrew text, most notably the proto-Masoretic text, which had become the most popular and commonly used text in Palestine. As we know from manuscripts found among the Dead Sea Scrolls around Khirbet Qumran and other locations in the Judaean desert, the LXX/OG began to be corrected toward a text similar to the proto-MT almost immediately."
"As the Jews were unsatisfied with some readings of the original LXX/OG, so were many Christians. It is a basic fact of historical and documentary evidence that the LXX/OG text of the Greek Old Testament did not remain a homogenous whole, but was for many centuries subjected to systematic correction by Christians."
"...there were a number of occasions when prominent Christian scholars systematically edited the LXX/OG correcting it back toward a Hebrew text."
"...the text of the Greek Old Testament that is in use today by the Orthodox Church came together over a period of some 500 years..."
"...we should be aware of the developmental history of the Greek Old Testament in order that we might avoid mischaracterization and absolutization that spreads errors in the name of 'Holy Tradition.'"
Notes from post 3:
"The variations between the MT and LXX can be analyzed more or less scientifically to determined how they arose. We need not rely on conjecture or baseless accusations that the Jews edited their Hebrew text, simply because we notice these variants."
"Casting aside the MT simply because it is not the LXX is short-sighted and unnecessarily severe."
Source:
Ancient Faith 
