Slide something thin in there like a business card or envelope
An envelope may be to flimsy, however a business card is a good idea. I will try that!
I have seen this seam on everyone's AirPods so it's obviously part of the design, no idea what for though...
I think it's the adhesive that is somewhat dirty. Other cases are worse than others. But mine is slightly tinted dark. But nothing to the extent that I've seen from others.
I don't have mine yet as I only ordered yesterday (March 10th delivery LOL) but I hope it doesn't appear as bad in person as it does in very close up pictures, I really have a problem with dirty gadgets if I can actually see the dirt.