From looking at all the pics on the net, I am wondering if the air valve is to charge the nitrogen gas, not an air valve to add preload? It didn't have any gas in it, and adding air didn't help.
It compresses ok but then takes a long long time to rebound, basically it stays stuck down while riding.
Closest match from hundreds of pics was a Bitubo brand, but not sure till I rip it out.
In any case, it looks like a good quality aftermarket shock, so may be cheaper to rebuild, than just get a new one.
Is there a motorcycle shock rebuild place in Perth? Or only RAD in Qld?
Deano