Rauner has one letter from Beethoven to Christoph August Tiedge from September, 1811. It's a small window into Beethoven's personal life and his interactions with friends and acquaintances. In it he discusses his meeting with Tiedge and bemoans the fact that they did not become friends sooner. He writes "Every day I blow myself up for not having to got to know you sooner at Teplitz" and goes on to mention that he would like to "hop over to the capital of Saxony" to see Tiedge again and that he has decided not to visit his patron the Archduke.
...I received a letter from my gracious and musical Archduke saying that...he was letting me decide whether I should go to him or not. Well, I put the best construction on this in accordance with my intentions and desires; and that is why you see I am still here...Beethoven then rambles on a bit about his room-mate having "got lost today...and so I could not claim his company." He closes with "I am expecting at least one word without any reserve, chiefly because I can take it."
The letter is in German, but a transcription is housed with the manuscript. Ask for Mss 811506.