I had the primary off my 700 Venture (1999) to replace the starter. Look what I found. I'm guessing the ring gear went and did it. Your thoughts???? Should I drill a hole ahead of that crack and hope it doesn't get worse? 
ya, one of the ring gear bolts must have came out and whacked it. I would lay the sled over on its right side and clean that area out well with brake clean, blow dry with compressed air. I would then mix up some jb weld and pour it in around the bolt and broken part of the case as so it doesn't develop a air leak and lean the pto cylinder out.