Thank you so much for linking that article! It was new to me, and not only does it provide us with a great summary of how that quote came into existence, but Luh actually provides me at last with the source for another, actual Fritz quote about MT, "Das apostolische Rabenaas". (It's from a letter to the Marquis D'Argens, and Luh provides a proper citation ( Friedrich der Große: Mein lieber Marquis! Sein Briefwechsel mit Jean-Baptiste d’Argens während des Siebenjährigen Krieges, hrsg. v. Hans Schumann, Zürich 1985, S. 134.).