Here he is – in Seminar Six.
“Yet Duchamp and his sub-tradition have demonstrated, as nothing did before, how omnipresent art can be, all the things it can be without ceasing to be art. And what an unexceptional, unhonorific status art as such—that is, aesthetic experience—really has. For this demonstration we can be grateful. But that doesn’t make the demonstration in itself any the less boring.”