Getting ready to install an '08 rear diff cover tomorrow and was reading that the axle holds a lil under 4 qts of fluid and that the factory recommends synthetic. I was planning on using synthetic from the beginning, but didn't realize it's $15 qt - it's only $8 qt for the 75w90 that my Camaro uses. So, not a deal breaker, but I saw that Lucas makes an oil that says it's suitable for all applications - I believe it was called something generic like "Heavy Duty Truck" formula w/ the picture of a semi on it. Anyone use it? Is it dino based or are Lucas products synthetics?