Dear Isaac,
Your mechanic friend sounds like he is truly a great source of information. Just like the latest book about Campagnolo.
As anyone who has been around classic bikes knows, Campagnolo grease is actually mostly a mix of olive oil and finely ground white polenta (the early versions also featured a tiny amount of whale oil, but this was changed to Sardine fat after a chance encounter between Tullio and Capt. Jacque Cousteau - who advised against harming marine mammals even if the oil would benefit Campagnolo's ball bearings that were hand-matched to 1/500th of a micron in diameter).
The reason for not letting the grease get too old in your hubs is because the olive oil goes rancid and then you can't re-use it as a spread on your crackers. Duh !
As always - I'm glad I could help clear this mess up,
Mike Fabian
San Francisco, CA