The 90 (black tag) ZF does have straight-cut gears, and they do whine a little, especially in first gear. And, I'm a little skeptical of bearing issues with only 22k miles; dang thing is hardly broken in!
Bill Boudreau is "THEE" ZF guru,
ZFdoc.com and on his web site he recommends the Castrol TWS 10W-60 synthetic which might be all that is needed.
And, I too had the same question re the clutch release position on my 95 Vette, and Bill told me then that was normal, and if it was otherwise,
that would be a problem.
Well, obviously, with only 22k on it, it has done its share of resting. Resting has a way of being very hard on seals, and bearings (drying out), etc. so I'll stop short of declaring phooey to a bearing issue. I'd want someone who has an early Z to test drive it and let you know what is normal or not.
In the mean time, do you hear it whine in higher gears? And, does it whine when decelerating with the clutch out? Either of these might be indicative of "something" not quite right. I'd want to check the trans oil level, and as you indicated, changing that would be the first thing to do after checking the level and see if that makes a difference. Again...bearing after only 22k??? The things that make ya say "Hmmmmm...."
Good luck with the easy stuff. If you pull the trans, you could benefit from the C-beam plates that Bill sells, if it doesn't already have 'em (
for easing the process of removing and realigning the C-beam, if nothing else!).
P.