embelton,
Now don't laugh this works, Mix some baking powder with a little water into a paste then lightly brush it on the contacts and you will see the green/blue corrosion coming off. I use this regularly on old LED calculators and watch contacts with great effect.
Finally I polish the contacts back up with one of these...http://cgi.ebay.co.uk/ABRASIVE-FIBRE-FIBREGLASS-PENCIL-PEN_W0QQitemZ9743810210QQihZ008QQcategoryZ296QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
I hope this helps...