For some reason LR axles decreased in strength A LOT, about the time they went to 24 spline on all vehicles (early '90's).
Ashcroft have tested genuine (1.24") 24 spline axles and found they break at about the same torque as earlier (1.1") 10 spline axles.
They went from making them from steel to making them from cheese.
Of course - the lack of proper lubrication on the defender doesn't help - which is where your wear comes from. Make sure you pull the inner seals to run oil lubrication.

