Unballanced clutch disc would make the most sense. Every time i floor it, its always made a thumping sound. Ill be switching to a brass bushing and a new prop shaft moveing foward. I was the one who put the clutch in 10k ago. Its poddible that i put the wrong grease in, been too long to remember but i know it came greased to start.
It was an LUK kit

 

Its the same type of bearing that's in the back of an alternator, and I have never had one of those go bad. Old and worn but not bad, goes to show it can happen. I had worked on an old Honda 70s civic years back and had the engine out and noticed it had no pilot bearing or bushing on a manual trans. And what I found was it didn't require one, at that time I couldn't find one that would fit. I always thought that was strange.

 

Without doing research isn't the outside diameter on a bronze bushing larger than the roller bearing? And is that a option? C-5s had the roller bearing and the C-6s had a ball bearing. I'm sure a bronze bushing could be machined down to the roller bearing size easy enough to fit. You have me courious I need to look into that.

 

Looking at 1980 Corvette at Rockauto there was the of bronze or roller bearing choice. It looks like they used the roller bearing back in early 80s that interchanged with. Answered my own questions.