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.
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.
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.