These score marks on the inside of the extension housing (diffy cover):
Indicate that the roll pin holding the spider gear pinion came out, and the pinion came loose, scoring the inside of the housing and eventually breaking it. This is a far-too-common failure mode on 4T6x, (and is accelerated by one-wheel burnouts and general hard-pounding the trans).
EDIT: It'* also possible that a spider gear cracked, or the pinion itself wore down and cracked, but anyway any of these things lead to what you see, and all are accelerated by burnouts / hard launching.
Drop the pan and see what'* in there and inside the filter (cut it open) before deciding what to do next.