Where you using it in conjunction with the expensive angular contact ball race upgrade to the clutch?
If you hold the clutch in for too long the old style release bearing heats up and the grease can be lost..
The angular bearing is designed for side thrust and is better to handle the loads. Must install the right way and its not easy to see !
Don't realy know whether the cone slips in the bearing as there isnt much contact area or if the bearing always spins.
If it slips you would get wear and heat due to friction - haven't seen wear but maybe heat colouration on the first.
I would not go back to the original parts - failure is more likely and more expensive.
The breaking that has been reported is likely due to machine cut threads weakness - rolled threads are better.