Delvac 5w40 is a great oil, but it's now called something like "Truck and SUV Heavy Duty" oil. Heavy Duty being the identifier for the synthetic (regular Delvac 1300 has been rebranded "Truck and SUV.")

In a motor that old/over 75k-ish miles you should go with the thickest oil to prevent leaks. You really don't NEED synthetic, but a great type for older motors is Mobil 1 15w50 with supersyn. Some Walmarts have stopped selling it because most cars and trucks are running such thin oil now. Look for it; it's usually about $20/gal

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL