A 1/2 inch socket drive fits.  I've found that the wobble type get a better bite.  The straight ones slip out easily.

Run a torch flame around the plug to expand the hole.  It's a taper fit, that's why it sticks out like that, and Nissan used a powerful sealant.  

Yeah I found the 1/2inch fits in the drain plug but It's the fill plug that I'm struggling to get to.

Thanks 

Oops.  I use a big adjustable wrench, aka Crescent wrench.

p.s.  I've found that a 12 point socket will often fit a four point plug like that one.  The six points won't.  But the grip is weak because the contact area is small.

There are 8 point sockets too. with the right size it should grip quite well.

https://www.grainger.com/product/1AX12?gclid=EAIaIQobChMI55P0wur36QIVSh6tBh25RwitEAQYASABEgJguPD_BwE&cm_mmc=PPC:+Google+PLA&ef_id=EAIaIQobChMI55P0wur36QIVSh6tBh25RwitEAQYASABEgJguPD_BwE:G:s&s_kwcid=AL!2966!3!264955915865!!!g!439063557338!

https://www.ebay.com/itm/221709332289

6 hours ago, SteveJ said:

I cheated and filled through the breather.

How do you when it's enough?

1 minute ago, grannyknot said:

How do you when it's enough?

Won't the overfill come out through the vent anyhow? He'll know it's full when there's a puddle. 

10 minutes ago, grannyknot said:

How do you when it's enough?

I read the FSM and put in that amount. I just make sure there is a way to let air out the breather as I fill through it. 

I think that you can fill through an axle hole also.  That square head is pretty easy to get the leverage on though.  Not sure why you'd not remove it.  No offense to those that didn't.

Oops.  I use a big adjustable wrench, aka Crescent wrench.

Yup, that’s how I did mine. Wrench on and two or three moderately hard hits with a 2.5lb hammer and she spun like a ballerina!

A 1 inch piece of flat stock about 10 inches long with a 1/2 inch bar stock piece welded to the end. The I/2 piece was measured to allow it to just fit between the mustache bar and the diff for a normal cover. You can also just weld the short piece of 1/2 bar stock to 10 inches of 1/2 stock. The extra capacity cover has a side filler and is somewhat easier to get at with a 1/2 inch extension.