Great find Barry, thanks. Motul is a trustworthy brand, I think, and seems to be widely available in China. I'm going to go for the manly stuff and order 15W. If that doesn't do it for me, then I'll definitely be taking up AW on his very generous offer (I have first dibs, folks!). Hmmm, i wonder if heavier oil would be more prone to blow the seals?

No idea about temp on fork performance.

Most manufacturers recommend changing the fork oil about every two years, or 20K miles. From AW's informative notation about discolored oil in one fork, maybe the JH600's original oil is not very good and the first change should be sooner.