Like many old BXs mine has the problem with the rear c pillar windows. They have a 'sun damaged' patch in the center.

I wondered why it only affected the central part of the panel - maybe only the part that lets light through? no, there is still an undamaged clear border around it.
Mr Rutherford says it could be a sticker that the early ones had that's gone all hardened and crazed.
Does anyone know for certain why it's so concentrated to the middle?
Any tips on how to improve it? it does scrape off to a degree but the improvement is marginal.