Central 'stripe' out of focus - Update

[droj]

The plate isn't meant to be dead parallel when the back's open, ie that's irrelevant in itself. It has spring steel legs that can slide on the retaining lugs, so it evens up when the back's shut. But make sure it moves freely, or even detach it and check nothing's bent!

 

[Craigus]

Yep it is a wear line. Though all four corners move as freely as the others. Very odd.