stumbled upon this..
just answering to complete the thread.
The Brown stain is the "electrochromatic" fluid in the glass that has leaked and has been "cooked" by the heating element. This is what developes the so-called brown stain. totally warranty as long as there is no signs of impact.
this glass is NOT cheap >>> hundreds of dollars BTW
It happens.. no big deal to replace glass, all though its a little nerve racking when pulling on the glass as one thinks it will break in their hands.
as said no tools needed per say but i use a plastic trim tool to aid in the even appliciation of force to pop the glass out of its clips.