non-replacable u-joints.

What kind of z do you have?

Have you confirmed that the u-joints are bad? Your post reads like you could barely tell from just looking at it. Good luck if the eyeball diagnosis works out.

You'll have to drain the transmission fluid when you pull the yoke unless you have fast hands. You might replace the output shaft seal if it looks leaky. It just pries out and taps in. And new fluid if it's not recent.

76 280Z, so non-replacable.

Zed Head, I got her on the lift earlier, u joints had grease residue coming out of them, with the ebrake down, I was able to rotate it on the lift and could see the shaft moving up and down. It's either the driveshaft or the rear end. (Un)fortunately I'm going to pull the motor tomorrow anyway for my RB20 swap, since tomorrow is the only time I'll be able to have the lift for myself.