I wanted to give you an overview of the state of the Torah text. I wanted to draw you a complete picture so you can see the degree of the problem.
First of all, there are only three available sources (witnesses) of the original Torah text, namely Masoretic Text or the text of the Jews (Torah scroll as you know it), Samaritan Pentateuch which is a text of a small Jewish sect and Dead Sea Scrolls (Qumran Scrolls) that are remains of another Jewish sect.
These three witnesses, MT, SP and DSS, are the primary sources of the Torah as we know it. You can find all three on my Interlinear Pentateuch project web site.
All of these witnesses come to us from the after 2nd Temple period and as far as I know there are no earlier sources of the Torah available. For example, it would be interesting to see the Torah from the days of the 1st Temple, and even more so from the days of Moses and Elders.
Masoretic Text is the most widespread and considered a standard and a tradition. However, Samaritan Pentateuch contains very important additions not found in the Masoretic Text.
Samaritan Pentateuch is closer to the original, except the famous 11th commandment (this part was obviously added by Samaritans).
You can find the list of most significant difference in the SP here, in this post.
Dead Sea Scrolls are closer in spelling to the SP rather than MT, but as far as text itself goes DSS are closer to MT. There are no significant textual differences or any important additions in the DSS - mostly spelling differences. DSS are pretty much useless when it comes to the Torah, so it can be disregarded for the most part.
However, even if you use all three witnesses together, you will find that the text is still corrupted. This means that many changes occurred prior to the 2nd Temple period. How do I know this? Through comparative analysis of the text. In many places text does not make any sense, which is an indication of intentional change and corruption. Here is a one example.
What does this mean? It means that you have to be very careful when you studying Torah, because the original text itself can't be completely trusted. Best way to get the correct information from the text would be through logic and comparative textual analysis. If you blindly trust the text, you will make mistakes in understanding the Torah.
All three witnesses were extensively edited, even the most holy parts like Decalogues (Ex 20, Deut 5). While some changes appear accidental and due to scribe not understanding what he was writing (i.e "work" vs" "slave work" issue), other changes look definitely intentional and sectarian in nature. Example with Passover above is one of such intentional changes to fit the pharisaic agenda.
So like I said, be very very careful with relying on just on the text of the Torah. It has mistakes too, so it can mislead you.