Most likely a cleaning chemical used on that surface has etched/damaged
it.  That plastic piece should be available seperately, is usually
relatively inexpensive and can shouldn't be too hard to swap out.

Cheers,
Nirav

Ammonia discolors plastic. No more windex.

Many instrument panel and most head light lenses are made of a plastic
called polycarbonate.  It is used because the strength of the material
(same material used in bullet proof "glasses").

The only problem is that polycarbonate does not have the chemical
resistance or sun light (UV) resistance that some other plastic
materials do, thus yellowing and fogging occurs easily... but hey, they
get to sell you the spares...

Good luck!