learsfool:
Yes, you are correct -- the Schumann notes say "horns with three rotary valves crooked in F."
BTW, we learned as musicologists that Brahms was the last major composer to specify natural horns -- and did so when most others were moving to valve instruments. Is this true? Are you familiar with any period recordings of the Brahm's symphonies that use natural instruments?
Keep buying Brahm's symphonies trying to find performances with in-tune string playing. His dramatic first violin leaps upwards never seem quite accurate and/or comfortable. The best I have found so far is the Zweden recording with the Netherlands Philharmonic. But Zweden is very cautious with tempi and the gestures never are molded the way Solti and others do so effectively. Let me know if you have any candidates.