I'm the new owner of a Black 2002 Tundra AC 3.4L RWD. It has 94,000 miles on it and I don't think the differential fluid was ever changed. I do not have an owners manual and have done some searches on the site, but I'm confused. Some recomend 75w-90 and others say 75w-140. I have also seen posts saying I should not use synthetics because of leaking seals. Any information on the correct oil and if can use synthetics would be appreciated.