Here are some more pictures of the removed IRD and CV
While a little blurry the splines inside the gearbox are all okay:



Not sure if it is how it is meant to look but the middle set of splines only have spline at the bottom of that part but the CV still splines in and rotates nicely.

All the splines look good on the IRD itself:
All shafts rotate okay, not sure if more disassembly is required to see if there is more damage but it all spins nicely without grinding or any bad noises:

The bearing on the small gear looks a little worn but nothing excessive as I cannot feel a lip on it.

The splines on the CV Axle look okay not bad, still there, none missing or twisted:
Albeit blurry I can confirm all the splines look okay, I took a look at the UJ's under the boots which looked good too.

Does this mean the Failure is likely to lay in the Trans/gearbox or in the CV which I cannot see/tell?

Thank you for all the help, just trying to work out what is broken and needs replacing

Though the more I look around and at the below picture:



The more I think it is stripped as the splines where the IRD would go (The smaller set of splines) it is smooth but with little bit of spline at the end. this picture illustrates this Red being the beginning of the splines, blue being what is left of the splines and green being smooth area.



Note that the blue and green does go all the way around.

This would mean I need a new gearbox right?

Thank you!