So first of all I want to state that I indeed understand Feynman's reasoning as to why the Brownian ratched fails. (At least what's written about it in Wikipedia.) I want to consider the following setup:
Now my question is: What would happen if we enclosed the ratchet mechanism (but not the paddle) in a vacuum?
I don't see how Brownian motion could now enable turning in reverse, so effectively we'd be left with usable work. This however contradicts the 2nd law of thermodynamics.
I'm only really interested the theoretical problem rather than practical challenges.