[richard-at-home]

Lack of a cutting fluid would be my best guess. A flood coolant system using a water soluble cutting fluid would be the best, but that is probably not practical for your system. A mist spray system would work well also. My next choice would be WD-40. Use a spray bottle or pressure can. The spray bottle is less costly.

Thanks Jim.

I will try some WD40 or a small amount of suds oil/water mix.

The finish was great for quite a while but suddenly changed. (pics in worng order, so inital finish is on the right!)