virtualbox.org

Seems the linked to the 5.0.30 > Extension Pack All Platforms has gone dead...

Downloads > VirtualBox older builds > VirtualBox 5.0 > 5.0.30 Extension Pack All Platforms

Prior release links work; but when installed, result in nag message on launch that a newer pack is available...

Can the link be corrected?

Try this link http://download.virtualbox.org/virtualbox/ instead.

Link is fixed. Looks like it was a victim of a little bit too generous search/replace.