This sort of problem has been with us for many decades. It is caused by paraffin reacting (congealing by chemical reactions) to normal heating/cooling cycles that every motor endures. Pennsylvania crude based oils commonly have paraffin in them, so if you avoid those brands that are made from Penn crude stocks, you generally avoid the problem.
I would also bet that oil was never changed !..lol. and yes, YOU NEVER KNOW WHAT YOU WILL FIND INSIDE A MOTOR WHEN YOU SPLIT IT ?!. I could write a book on odd stuff I found inside motors that I've split !..lol.