Originally Posted by Numinous
@ apocalypz: only the Zetsu coat would modify his chakra signature of all the arguments you made and it would be a non-issue if Minato was a sensor, considering Ao and Karin were able to distinguish different chakra signatures within the same person (Danzou and Naruto respectively). Considering that, if he was a proper sensor, he WOULD know Tobi was Obito. Since he didn't, the logical thing to assume is that, if he senses chakra at all, he's very inexperienced on the matter.
Correct me if I'm wrong, but we don't know how long those Zetsu clones have been attached to Sasuke (prolly put on him during the Kage summit when Sasuke was running low on chakra and Zetsu replenished it). But if that is the case, Karin and Ao never stated nor showed any knowledge of those clones being on Sasuke. They only read Sasuke.
Isn't one of Zetsu's specialties making it's chakra signature resemble whomever it wants. I'm assuming that Obito was wrapped in that Zetsu clone during the kyuubi attack on Konoha, hence concealing Obito's chakra signature, and possibly giving off Madara's. We've seen how the Zetsu clones can mask anyone's chakra signature and fool the sensor corps.
P.s. Thus far, the only two uber sensors have shown to be Naruto and Mito Uzumaki, sensing will and feelings and what not.