I am acquiring a 2002 pontiac bonneville with 160,000 miles as a work vehicle, and wanted some of your personal recommendations for these engines. I have been out of the "gas loop" discussion for awhile now, and have spent most of my time on here lately in the diesel oil section. I know some will say "follow owners manual" and "these engines will run on anything"... so don't flame me for asking please? The previous owner told me he ran pennzoil conventional it's first half of life, and then switched to pennzoil platinum. Uses a quart in 5,000 miles. Should I stay with the platinum and extend the interval? Do any of you think the pennzoil high mileage oil is a good option? I would like to run a UOA before I think about extending any oil to see if coolant is present in oil, as I know these engines have leaky intake gaskets. -Thank you all in advance.