The viola part, particularly in the first movement, is frequently played overly staccato and too softly but frequently it is this middle voice which is responsible for many of the harmonic delicacies of the piece. The joviality here is real. It is as if happy thoughts are a thing remembered. Here is a sample of the score, the whole score is posted to the Member Files area of the Conduct list at E-groups. You need not be a member of the group to access the files.
Parts are available.
25 for Flute, Violin and Viola. This is a 3 page sample of the score. You need not be a member of the list to access the files. Parts are available. Of these possible six Bach concertos only three have survived to the present day.