Thanks for that. So it sounds like dirt/oxidation can cause the excessive sparking, which then contributes to pitting of the adjacent surfaces. Presumably keeping the electrical contact surfaces clean will reduce sparking and the possibility of pitting.
Makes sense. I run prewar gear predominantly and I haven't noticed much in the way of pitting (or excessive sparking). I am, however, guilty of running stuff until it's absolutely filthy, so I likely need to do a better job of keeping rollers/shoes and rails clean.
PD
