Wikipedia has a very short description of the Third Movement, which reads:
Described by Goodwin* as “virtually an ‘operatic’ ensemble of passionate feeling and sensuous warmth”, the third movement, marked Adagio, is in E flat major. A syncopated pulse occurs almost throughout the movement while solo lines alternate between the solo oboe, clarinet and basset horn.
* Noel Goodwin, CD liner notes for Mozart: Three Wind Serenades, Sinfonia Concertante, ASV CD COS 242
However, it is in clips such as the following that highlight how woeful my musical education has been (despite all my years in performing). F. Murray Abraham (in the role of Antonio Salieri) describes the beginning of the Third Movement in a way I would find very difficult, if not impossible, to do -- and wish I could.