so i got this car back in September with 58000 miles on it. ever since i had the car i have not put new oil or add oil to the car. and each time i check my oil level, it is fine. i been getting mixed reviews on often i should change my oil. right now i put almost 9000 miles on my car. so i was curios what yall think and does it matter what brand 5w20 i put in as well?