[Steeveedee]

I never heard of the charcoal dissipating. At some point in its life the charcoal must have been dumped out. The fuel vapors adsorb onto the surface of the granules and are then pulled away by engine vacuum. I stopped working as a mechanic (for a living, anyway) in '84, and never saw an empty canister. But then, they were at most 13 years old.