In my lesson I played the Bach P&F in E flat from WTC Book 2, and after playing, my teacher looked at how I fingered the downward E flat arpeggio in the first measure (and througout the piece), which I played as (going downward, in LH) 1 2 4 5, and he said that I should play all LH arpeggios/chords that begin with a major third (going up) as 5 3 2 1 and a minor third as 5 4 2 1, because sometimes in pieces you have to play a minor chord (5 4 2 1) to a major chord (5 3 2 1), only changing the third from minor to major and holding all the other notes.
Thoughts?