Mobile 1 synthetic is about $20 for a 5 quart container at Walmart. I've been using it since 15k miles, changing oil at 5000 mile intervals. Currently, I have 185k on my truck. It runs great, and I never need to add oil between changes.

MaxLife is available in Synthetic, it's $5 per quart at Checker Auto.

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From Valvoline's website:

Unlike regular synthetic oil, MaxLife Synthetic is advanced synthetic PLUS special additives to fight the effects of aging. If you use synthetic motor oil in your engine and it has 75,000 miles or more, then MaxLife Synthetic is right for you!

MaxLife Synthetic helps extend the life of engines by providing:

Special seal conditioners to help keep engines cleaner and reduce oil consumption
Additional anti-wear additives to reduce friction and help prevent future wear
Extra cleaning agents to help reduce deposits, sludge and varnish formation
Advanced thermal stability to help reduce oil burn-off and maximize power output

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