I think it's pretty clear what Orochimaru truly was seeking and that was So6P power. Think about it, he knew all about the Rinnegan and Senju and Uchiha DNA mixing. His earlier vessel was Kimmimaro who we learn was a clan relative to Kaguya then when his body failed he went after an Uchiha which would also lead him to the Sage's power. Everything Oro did was to reach the sage.