I recently changed for the first time the rear differential oil in my 2002 V6 Ford Explorer and quickly rechanged it from Lucas full synthetic 75W140 to Amsoil severe gear 75W140. I was throwing out the empty bottles and noticed that the "sulfurous" rotten smell of gear oil was significantly more pronounced in the Amsoil that the Lucas. Perhaps the add pack in the Amsoil is larger than the Lucas? In any case, it certainly smells worse!
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