The most important specification in motor oil is the “weight”,or grade, because outside temperatures will vary seasonally. Typically, you want an oil such as 5W30 for winter use and 10W30 for summer use where temperatures get very high. Your manual may say use 5W30 all year round. I would agree with that if you live in Seattle or some other pace with moderate temperatures all year. Your Olds at 98,000 miles is still a “spring chicken” and if you have changed the oil regularly, there should be very little engine wear. My wife’s Nissan has 115,000 miles on it and does not consume oil, and has its original compression readings.