Is there a reference to what Goss has actually done? I have seen nothing and at a certain point one has to become skeptical as to his effectiveness given the frequency and magnitude of these leaks.
I have no idea what he's done, but I imagine that house-cleaning would be difficult. Think about this: You have an employee with no loyalty to the US who has been leaking to hurt our interests. You fire him. Now what do you think that employee will do? Keep his mouth shut or spread more damaging information? Plus I'm sure these guys have no problem telling lies to advance their agenda and damage their enemies.
Another problem is this: If you want to prosecute, you need ironclad evidence. Just knowing that someone is a dirtbag is not enough. So you have to keep an eye on them and gather proof of their crimes.
The best work against these rebels is done in the dark, I think.