I need to change my transfer case oil and will go with an Amsoil gear lube. Three of their gear lubes are suitable (80W-90 Synthetic Gear Lube, SEVERE GEAR 75W-90 Synthetic EP Lubricant & 75W-90 Synthetic Long Life Gear Lube)but I don't normally see anyone make reference to a specific Amsoil gear lube. What would be considered to be the best Amsoil g lube for a requirement for a GL 5?