Ok guys, I just came back home and had another look at it... and... it's really just nothing... I mean, there's just no way that Apple would replace the entire machine just because of this tiny fault.
I took two more pictures, this time in clear light, just to give you an idea
🙂
Here it's totally invisible (I had to use the flash, the picture would have been too grainy otherwise
You can barely see it as a dark "smudge" here
I would feel embarrassed to point this out, so I'm going to keep it. I'm really happy with the machine and I feel that we've already "bonded" anyway
🙂 Also, everything else is in perfect condition. No dead pixels etc.
BUT, I will still call Apple, just to see what they have to say. In fact I'll call them right now
🙂
EDIT: The guy at Apple said that it is covered by my warranty. It didn't seem to matter how small the damage was. Still, I'm not going to bother with it, I don't want to risk getting a computer with other faults.
Thanks for all your replies.