What are you trying to get at when you say "what happens to test probes when height is not set right and are overstocked?"
Is a black coating or coloration on sliding part of the probe normal ? I wouldn�t call anything normal when it turns gold plated test probes black. Should you expect to see it if you�re running NC flux? Ubetcha!!! Is it an insulator? Ubetcha!!! Does it affect the continuity between the probe and the outer-contacts on the test probe? Ubetcha!!! Wudyagunnado? Tell me where you buy probes and I�ll buy stock in their company.