Lets answer two points that are wrong:
1. Have the OT manuscripts been changed.
Likely. One only needs to compare the LXX to the Masoretic text to see this. While in the past many held the MT to be older now that is slowly falling away. Indeed the Septuagint is shorter in many places and besides that>>>>
2. The Torah predates written Hebrew language...WRONG! The oldest texts in the bible are from Judges 5 and Exodus 15 and possibly Psalms 45. The former two are in very old Hebrew predating 800 BCE but not going before 1000 BCE. The majority of the books from Genesis-2 Kings shows major Hellenistic influence from the beginning to the end. (Even the creation story in Genesis 2-3 is pulled not from the Epic of Gilgamesh but from Berosses Histories (which uses the Epic))
I will also mention that the Dead Sea scrolls community were a cult even weirder then Jehovah's Witnesses and their changes to any texts were more messianic and Apocalyptic then anything. The books of Enoch and Daniel were likely from that community.
As for Hebrew being the original language that is kind of laughable since the older languages are well known.