This video of Steely Dan's "My Old School" is, I believe, from a 1973 episode of American Bandstand, and serves as a good introduction to what used to be conventional in terms of lip-syncing. The Dan brought along, in addition to the core five-man band of that time, a three-person phalanx of background singers, but not a horn section, even though "My Old School" has a pretty extensive horn part, including one passage where the horns take the lead. If they weren't going to bring anyone to fake-play the trumpet, why wouldn't they just get Becker to pretend to sing the backup parts? Somebody had to pay all those background singers!
Dick Clark's henchmen put Fagen and Becker upfront, obviously, because they were the leaders of the band, but it's strange to see the piano out front like that, with the bass player right behind him, especially since Becker evinces no interest in miming the song, and stands there like a gypsy queen in a fairy tale, plucking his bass every once in a while and looking most bored.
It's also a little jarring to see these guys when they were so young; they've been curdled yet sophisticated for so long that you never think of them as being a day under 40.