I have a 1986 740GLE Turbo Diesel wagon and need to change the oil as it has around 107,000 miles. I'm not sure what kind of oil the Volvo dealership used when I had it changed 4,000 miles ago. Since it has over 100,000 miles and is a diesel, would it be best to use 5W-30, 10W-30, 10W-40, or...