Hi Raid,
That news item (stemming from an email exchange I had with Chuck Westfall) applies only to lenses not officially designated as weather/dust resistant (the 24-105L is so-designated). You can identify sealed lenses by the rubber gasket at the lens mount, and lenses with that gasket also have sealed switches and zoom/focus rings. The point of the news item was that some lenses ( the pre-1999 white ones), which lack the mount gasket, do have sealing at the switches and zoom/focus rings (this isn't commonly known), and are thus partially sealed (as opposed to 'fully sealed').
Hope that clarifies...
John





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