[...] I have just learned that you have declared it impossible to engage Herr Seidl for your opera. I beg you, notwithstanding, to make it possible. In this I am thinking less of Herr Seidl (for whom I can at this moment find a good post) than of the Leipzig performances of my operas and—I know what I am about. There is not a single conductor who knows my tempi and the relation of the music to the action. But I have instructed Seidl. He could also conduct The Nibelungs for you better than anyone else. If these words of mine are not enough to influence you, I shall have no more recommendations to make to you in future.
(God grant that Unger lasts out for you! I heard a bad account of him in London!) [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 712