Welcome, Saber05, I would go as far as to say you don't need Dexos oil. Your car was sold a long time before GM came out with the Dexos standard. Use any API certified 5w30 oil, changed regularly, and the 3800 will outlast the car 19 times out of 20. What you should focus your attention on right now is the transmission. The 4t65e transmission in those cars can have some issues including some solenoids going bad which can mitigated with keeping up on transmission fluid changes. At 69K miles, it's due for a change unless you know it's recently been done.