Just watched this Toraguchi Tuesday video (name inspired by Waza Wednesday? if so, well done, Noah :)
It shows the middle part of Seienchin (or Seiyunchin in Goju Ryu) as being a Kata Guruma, or Shoulder Wheel throw.
For reference, here is the Kata (very close to the way I practice it. the relevant motions are at 1:28-1:34):
And here is the Toraguchi take on it: