my gear box in my valver has done 126k miles, and its sweet as a nut. a bit clunky in 2nds gear when cold, but apart from that its fine. depends what kind of driving you do, whether its town driving, lots of gear changing, and full on 8k rev limit action in 1st and 2nd. thats what kills them off, not jsut ren boxes. treat then well, change the oil every 20k miles, and itl last ages.
jimbo