Thank you so much Ching, the car is still working and it is no hurry. I just review the Xray manual, it mentioned the kit included a graphite rear axle shaft but the kit comes with an aluminum axle instead. And I just want a more reliable graphite axle shaft for less maintenance.
All new kits comes with aluminum axle now. There was a problem with xray's graphite shaft before as the screw comes off the graphite shaft too easily.
As another c-hing mentioned, you can replace the axle and the right wheel hub with another brand and fit into the xray as this may be more cost effective.
Thanks a lot for your explaination, I didn't know the story of the graphite rear axle before. And I think it is better to change to other brand graphite axle. Because I hate to find anything wrong when I was in JV.