As a note, there is no way I am replacing the whole transom. First of all, it's pointless and a waste of time so why bother. Second, the affected area is very small. It is the area stemming out of the drain plug rot, in addition to the area near where the rotten center stringers attach to the transom. It barely even makes it to the keyholes. My plan of action is to cut the aft portion of those center stringers out for now, though I will glass them back in before filling the seacast fill of the stringers. This will also allow me to gut the stringers better as the tops are solid, while the bottom is mush. But a question I have is what is the best tool/method to cut out the bad parts of the transom without harming the hull?