Mystery interior panel damage

[Phase 1]

I have a 99 Explorer sport and since I've acquired it it's had this weird ? around both side mirrors on the inside. The pictures don't do it justice but the plastic is coming off almost powdery. I'm not entirely sure what's causing it but my guess would be washer fluid from the previous owner while the windows would be down? The lovely west Texas heat might be having an impact too. Curious if any of y'all have ran into this before and if there is any way to fix it or prevent more of it?

<a href="http://imgur.com/SUzGLz0"><img src="http://i.imgur.com/SUzGLz0.jpg" title="source: imgur.com" /></a>

 

[Frank1669]

Its the type of plastic- I am sure it is from the sun. I have owned several 73-91 square body GM trucks happens to the door panels often on those trucks. only cure is replace or sand off all of the loose plastic and repaint. but you loose the texture that was there,