axel code H9 so it's a 3.55 w/ limeted slip.

I've never seen anything like this before the hole housing that holds the diff broke into two pieces and screwed up my ring and pinoin gear.

I took the old POS out and have not taken the pinon out yet. $700 from summit for the Ford racing Hd unit and new gears and the installation package. Ok now for my question.

Where does an O-ring go I found a broken O-ring in the case?
Are there any tricks with the install.
What type of fluid should go with the new unit?