I can't tell you much. I had some HDKs in there, not done many miles at all, no issues, no noise, no violent tank driving episodes and I was backing out of the drive when there was a pretty horrid crunching noise and all sorts of screaming and screeching. I pulled the CV and essentially it had exploded. The bell had split right from the lip of the cup to the shaft. The night before I had been driving in snow and stopped to winch a bloke back onto the road out of a verge. Nothing dramatic. Now, like some, I don't think that one failure should condemn all aftermarket CVs to the trash. But, I was building a vehicle that I wanted to rely on so I put Longfields in there and in this current build I put genuine CVs in. In part I didn't want to give HDK and Milner more money after buying 2 from them and not getting a refund. I appreciate that aftermarket ones are probably going to be a consumable if you hard core off road, but for on road use, I would expect, say, 25k miles out of one at least.
I had an old worn out genuine CV and I tried to cut it. It was like armour plate. Very very hard to even score it. The HDK on the other hand, I sectioned with a hacksaw. Now, maybe there is an opportunity here for someone in the know to take something like an HDK which incidentally are very nicely made, and take them apart and have them heat treated perhaps. Maybe face hardened. Quite possibly we could get much better CVs for a fraction of the price. Why are the Toyota ones so expensive? Tolerances? Production methods? Material? I don't know. But it's a thought. A specialist heat treating company may well be able to do something, especially if they knew what steel they were made of. They could section one and analyse it. They should not simply be plain steel. They need to be special steel or SG iron. We don't want them too hard and brittle but too soft and they deform under load and that leads to failure.
Any metallurgists out there? What do they sell in Oz?
past the oil seal and into the diff oil? 
