Question
Has the text of the Bible been preserved exactly?
Answer
In many places, the Talmud, the Midrash and the Rishonim appear to have had different spellings or punctuations of words in the Tanach than we do. For a long list see Gilyon Ha-Shas on Shab.55b. Some of the discrepancies may be due to quoting verses from memory, but many of them seem to be due to differences in the masorah (the tradition about the text). The Bible is of Divine origin, but since G-d gave it to us, the preservation of the text has been in human hands. It has been preserved very accurately, but total perfection is not possible for humans to achieve.