I assume its a vent on top of my diff, very loose and plasticcy. Is this normal? It wont pull off or screw off it just spins

TA

Yes thats your vent.

You can get it off with a small pry bar the top will probably pop off first then you can get the other bit out og the axle. As Haynes say reassembly is reverse of removal but tap it back in place with a soft facede hammer.

Caber

It's a breather. Why do you want to remove it?