I've replaced mine on Redline MTL @70K and it turned out to be a not so good idea. The 2nd gear was touchy when I even got the car. I learned how to drive a stick-shift on it, so it clearly didn't get better
After the oil replacement things gradually turned out to be worse, much worse. 1st to 2nd started grinding occasionally, especially on cold starts, so I had to be extra careful. I have read and re-read the manual, it was quite confusing, but looks like the gearbox requires the weight 90 gear oil. People were saying the the regular gear oil is bad for trannys, I've got Royal Purple which is supposed to be compatible. After the change shifts started turning to better, although still not as good as they were originally.
When I drained the original oil, by the way, it came out clear. So I would not rush to change that oil, unless you know exactly what to put in.
Which brings me to the original question: what to put in the manual 6 speed gearbox? W90 gear oil?