Since we're sharing, I'll let you all know what i've got. i jsut replaced my gearbox due to a naughty drive shaft shearing at the uni joint and punching a hole in my '98 R33 GTR box. I picked up a '94 R32 box (identical, just older) from a very nice chap. he told me the box was reconned at 25,000km before he got it, then he replaced it with a dog box. I get whine in 1st, 2nd 3rd & 5th, and it crunches into 4th if i shift to quickly. I also have a lot of clutch noise at idle in neutral.
The good news is the box feels awesome, shifts well (except 4th sometimes) and the car doesn't have any vibrations or shudder or anything. I've put 75W90 oil in it, and i'm going to try some additive ot bring the noise down. After that i'll try a thicker oil or redline oil.
So I don't think it's a big problem, but i'll let you all know in 6 months if it's worse, better or still the same