As I have said before, I have been using a wc spindle for over 10 years, sometimes for prolonged periods. I run this spindle without water and it never gets hotter than hand warm.
My spindle is not Chinese, but was made in Germany by Jaeger back in 1985. I did discuss water cooling with a spindle recon company, and their comment was that if the spindle was only was warm no harm was likely to occur. G.