j'aurais dû followed by verb infinitif
Il aurait été followed by verb infinitif
I was very proud when I worked those out by myself from obeservation, listening then trying them and gauging the reaction, it was the first real milestone of my informal learning after my lessons stopped, given your level Mint I am surprised you did not conquer those a long time ago but perhaps you are following structured learning, profs dont like helping you run before they think you can walk.
I recall early on wanting to get to grips with coulda shoulda woulda!
Eurotrash, you make a good point, I need to revisit my learning and be able to differentiate between the two nuances.