As an aside to all of this but slightly relevant…
I am employed in the mining industry I guess at a reasonably senior level some would say, I am not a Mechanical Engineer, but have a few I manage directly and access to many on a global level, some might say what would they know about this but hey we somehow manage to maintain a fleet capable of 200mt of material movement a year and fixed plant that processes 28mt a year, so we have quite a few driveshafts gearboxes and couplings… plus 300 odd light vehicles and light trucks, predominantly Toyota.
We plan for replacement before failure due to OEM specification sometimes, but mainly our own and our monitoring and inspection processes are far in excess of the local Ineos dealer and manufacturers, quite simply we do better than OEM, we have to be. And we are profitable… in an industry where reliability is everything.
OEM make money from parts not original sale.
I collated some info from here, around the web and my own experience with my Ineos and presented this problem to some very learned people, from graduate engineers to 40 year veterans.
Most laughed and a few groaned, how could anyone design something like this was the overall response… angles, joint used and alignment all a risk, and contributing factors to a short life span and failure certain.
Only solution that was agreed was a redesign to improve the angle and alignment, which of course is both a new transfer case and differential location.
Oh, and if you want reliability use universal joints.
Just some encouraging insight.
FYI despite being exposed to Toyota globally and seeing many of them survive the interesting driving technique and conditions around Africa, I privately still chose to lay under a Defender for many years and hoped Ineos was a worthy successor, I guess it is from a laying under perspective… I am quite adept at driveshaft removal/replacement…