iMac 20" with dark screen corners

[rodti]

I've got an iMac 20" Core Duo which is about 15 months old with no Applecare. Since last year it has had the tiniest little 'smudge' in the bottom left hand corner of the screen, but it was so small I didn't really worry about it. More recently this grey smudge has started increasing in size, and similar grey 'splodges' are starting to appear in the top left corner. This is really going to harm my otherwise pristine iMac's resale value, and I'm out of warranty. Do I have any recourse via Apple as this is clearly faulty by design? There appear to be quite a few instances of similar problems on the Apple discussion forums but it's doesn't seem to be an officially recognised issue.