I want to thank everyone for their suggestions.

After much fiddling about I eventually pushed things beyond repair,  
so had to start from scratch after all - no big I had a backup so  
that is good.

So I took the opportunity to play a bit with mdadm (adding, removing,  
repairing, etc) and think a crisis will be averted should a similar  
problem arise in the future.

regards,
-m