What’s the Plural of Quid Pro Quo?

If you’re keeping count, which you should be (or leaning on us to count for you), there are now three quid pro quos in President Donald Trump’s orbit of impeachable corruption, or one giant quid pro quo with three distinct parts. We’ve named and itemized them, but is the plural quid pro quos or quids pro quo? Or quae pro quibus? Or quæ with the squished dipthong? Trump’s multiplying misconduct and favor-for-favor political dirt dealing are straining not just Congress’ enforcement of the Constitution, but copy editors’ enforcement of style guides. What’s an editor to do when the Associated Press Stylebook and Webster’s dictionary appear silent on the most pressing plural question of our time? You appeal to a classics professor.
“I would say quid pro quos, personally,” says Andrew Garrett, professor of linguistics at the University of California, Berkeley, in response to an email I subject-lined “on deadline.” “Nobody would get a Latin plural” like quae pro quibus, which “would entail more than one thing for more than one thing,” he says. “If we’re talking about Ukraine, is it one thing (a visit) for more than one (two investigations? or just one?)—or two things (also aid) for one (one investigation)?”
Let’s rule out quae (nominative plural) pro quibus (ablative plural) and quæ pro quibus. Two down. What about quids pro quo, like attorneys general? I could deep-dive the etymology there, but Professor Garrett was kind enough (and in transit). I’m not going to email agæn. Verdict: quid pro quos.