It looks to me like the ‘glass’ is delaminating. I presume what we’re seeing is the front, lower corner of the windscreen but is it Perspex/Plexiglass/acylic or Lexan/polycarbonate? I’m guessing polycarbonate because I think that can happen with exposure to hydrocarbons while I believe acrylic may craze but not delaminate.
Socata painted a stripe of that grey paint on the inside of the window, to hide whatever messy stuff is underneath that part of it (some bits of the airframe).
In various places, not just where the pic shows, this paint has come off the window material.
If it is just that, I am happy to leave it because it is just cosmetic, but one doesn’t want to leave corrosion getting worse.
It turns out that there is corrosion in the aluminium underneath the plexiglass.
It isn’t possible to get rid of it completely without removing the entire window, which is a very big job, which would take several days. One would take the opportunity to install a thicker window, for which there is an STC or PMA.
I managed to lift off the bit of the window visible in the photo above, and clean-up under it.
The cause is water entry here
