Thank you all for your quick and helpful replies. This morning I cleaned the area better than it had been. I used a dry paper towel and then I wet the paper towel with a dab of coolant to carefully wipe down the areas. I inspected the radiator top and cap area closely with a magnifying glass and with my finger. No cracks I can detect. The cap surface and the cap inside area clean and smooth now. The precipitate from the coolant is pretty abrasive and granular when it is left behind. I made it as clean as possible. Now I am doing a few cycles of the engine from cold to hot and over again and looking for any weeping. So far none. Maybe the residue was leftover from previous work or cap replacements? Hopefully. I will let the group know.
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