The biggest problem with throwout bearings today seems to be in the low quality grease they are filled with. It's just doesn't do the job, and the nature of the design makes it difficult to wash out the cheap grease and refill it with a high quality grease.

1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)