Currently I'm working on the volume concerning original and actual sin. I just sent off a long section on concupiscence. Perhaps that does not sound too exciting - but the argument between Rome and Wittenberg on this topic could not be of more contemporary importance. Is our inward tilt toward sin, our desires, our inner brokenness really sin? Or is concupiscence not really sinful? This argument maps onto the current discussion in the Christian world concerning homosexuality. Gerhard has all the ammunition you need: Scriptures, patristics, clear reasoning, history, etc.
Here's a snippet from Gerhard on venial and mortal sin - another long lost Lutheran distinction that would clear up a lot of thinking in our ministerium.
That some [sins] are called venial and only some are called mortal is not because of the nature of the sins but because of the mercy of the Father, the merit of the Son, and the sanctification of the Spirit. This distinction does not pertain to all people in general but only to the reborn. It is not to be taken from the Law which accuses and condemns all sins regardless of their type and size, but from the Gospel which demonstrates that sins of weakness and ignorance and corrupt lusts are not imputed to those who believe in Christ if they resist them; that is, if the reborn,
(1) acknowledge these evils which dwell in their heart;
(2) grieve seriously over them;
(3) ask and believe that they are covered by the merit of the Mediator as by an umbrella;
(4) by no means relax the reins ujpon them but resist them by the Spirit, crucifying the flesh along with its desires [concupiscentiis].
These four chief points are very correctly assigned to remission and mortification in the Apology to the Augsburg Confession.
I know the books are pricey (and I don't get any royalties, alas), but if you buy one volume a year and commit to read through you will plug a lot of gaps that your MDiv did not fill.