The passage quoted by Seth Ackerman is another reason why, as fascinating and suggestive as the Grundrisse may be, they cannot be understood as Marx's final word on *anything*.
All the more bizarre that Toni Negri presumes that the Grundrisse are the more authentic representation of Marx's thought. Then again, Operaismo is a pretty dodgy school of interpretation anyway.
But then, Charles Brown on this list is also prone to quoting the Feuerbach Theses like scripture, which proves that orthodox Marxists and supposed "heretical" Marxists have more in common than they think.