What would you use in a 95 Lexus V8 with about 90,000 miles? I recently purchased the car so do not know history. The engine seems tight--does not leak or burn oil. The car is used only in summer for highway driving and is used less than 7500 miles a year. The cost of oil is trivial but cost repairs on this car is outrageous and I'd like to keep it for another 50,000 trouble free miles. I have been using conventional oil but have been careful to always use a geniune OEM filter. Have not used synthetic due to concern over potential leaks. This is probably a myth but I have left well enough alone.