So, it turns out you need a vent on the differential and the parts can be hard to find. I am lucky in that I believe the little silver plug which goes in the diff and the vent then attaches to came with my kit. I think these are the parts numbers FR3Z--A & 2L1Z-4022-BA. I haven't actually ordered the vent itself yet, I'm hoping it will turn up in one of my boxes. It looks like a little black rubber hose. Here is the plug thing.



And I think it goes in this top right side hole.



I forgot to take a photo with it in. I'm tempted to tap it in with a hammer. Someone said to use red loctite but I haven't done that yet.
In this next photo I am pointing at a threaded hole which I think is dead ended but I'm not sure what is supposed to thread into it. Does anybody know?