Although I know you can unlink the sound from an event by hitting "U", I cannot see how you re-link other than to hold control or shift while selecting and then I seem to have to do it all the time as the event will not seem to re-link automatically. Quite often I wish to extend the sound longer than the video and then move the event around the timeline with the extended sound & video tracks linked together. - Is there a simpler way, as I cannot find ANY reference in the manuals about this or am I not up with their jargon ?

Ignore Event Grouping (a toolbar icon or Ctrl+Shift+U) is the option you want.
Enable it (ungroup), stretch your audio, disable it (regroup) and slide the grouped event around as desired.