Augustine does not have any comments on the Hebrew text for Exodus, Leviticus, or Numbers, so we turn to Deuteronomy.
Question 3 on Deuteronomy 3:11 (p. 371)
At Deut 3:11, the Hebrew word rephaim appears, which the Seventy transliterate. Augustine says that those who know Hebrew say that the word means 'giants'. Here Hebrew is a help for exegesis.
Question 20 on Deuteronomy 14:28-29; 15:1 (pp. 386-88)
The passage concerns the poor tithe: every three years, instead of going to Jerusalem and eating your tithe (Deut 14:22-27), you're supposed to dump your whole tithe into the middle of town for poor people (Levite, alien, orphan, widow) to eat. Or, at least, that's what the MT seems to me to indicate (the poor tithe replaces the regular tithe every third year). For several reasons Augustine finds his Latin translation of the LXX to be unclear about the distinction between this tithe and the other one that you're supposed to offer every year. So, Augustine quotes Jerome's translation for this passage; he doesn't name the translator, he just says in ea interpretatione quae est ex hebraeo apertius hoc distinctum reperimus. This translation from the Hebrew is clearer because it clarifies that the poor tithe should happen "in the third year" not "after three years," and it is clearly labeled "another" tithe, in addition to the one already consumed by the worshipper in Jerusalem. This is an interesting decision by Jerome, to insert the word aliam before decimam (not exactly reflected in the Hebrew text) with the effect that Deut 14 commands two tithes to be given every third year. This is not the way the Rabbis reconciled Deuteornomy's tithing laws, but Augustine seems convinced by Jerome's translation; he clearly thinks this is a more precise translation from the Hebrew. Augustine does not comment on why the LXX is unclear in the tithing law.
Question 54 on Deuteronomy 30:11-14 (pp. 413-14)
This Deuteronomic passage is the one about the Law being near you, in your heart, not in heaven or across the sea. At the end of the passage, the LXX says:
The word is very near to you, in your mouth and in your heart and in your hands, to do it. (30:14 NETS)Augustine recognizes that the Hebrew text does not have the phrase "in your hands."
nec frustra tamen hoc a septuaginta interpretibus additum existimo: nisi quia intellegi uoluerunt etiam ipsas manus, quibus significantur opera, in corde accipi debere, ubi est fides quae per dilectionem operatur. nam si forinsecus ea quae deus iubet manibus fiant et in corde non fiant, nemo est tam insulsus, qui praecepta arbitretur inpleri. porro si caritas, quae plenitudo legis est, habitet in corde, etiamsi manibus corporis quisquam non possit operari, pax illi est utique cum hominibus bonae uoluntatis.
But I do not think this was added by the Seventy translators to no purpose: unless because they wanted it to be understood that even the hands themselves, which signify actions, ought to be received in the heart, where faith is, which operates through love (Gal 5:6). For if those things which God commands are done externally and are not done in the heart, no one is so stupid that he will judge the precepts to be fulfilled. If love, which is the fulfillment of the law (Rom 13:10), lives in the heart, even if someone cannot work with bodily hands, there is still peace to him with men of good will (cf. Luke 2:14).That's the end of the discussion. Augustine appreciates the addition of "hands" even though he obviously considers the heart - already there in the Hebrew text and retained in the LXX - to be the more important element.