My friend who does some failure analysis for cat looked at mine, said that it had been cracked for quite a while. He said the section of break that is more polished has been that way a long time and the rough ridges were more recent.
Similar happened to that t case also, caused a ton of wear. The shift forks were worn out, the pads were completely gone etc. it just progressively got worse. I would say take it apart. Shouldn't cost much to fix