Or it could just be normal wear on a 30+ year old rotating part.

Maybe....but I can't say I've heard of it happening before.

"I will say that I love hard cornering, and had 3 track days last year. But I wouldn't call that abuse, and one would think the car could take that occasional stress."

umm keep in mind this is a 32 year old part. Plus the half shaft, U Joints on ends of half shafts, bearings, ect. are some of the hardest working parts on the Z. I know it's not a cheap part but If I were you, I'd bite the bullet and just go with a new one. There are just some parts that aren't worth taking the risk going the used route on. Go new like your dad did with the other side yrs. ago and be done worrying about it

I don't know how tight your budget is but thats just my thoughts.

Wouldn't be a bit surprised if it isn't available.