You've already lost that argument.
I'm one of the people who buys engine oil for their cars at Walmart.
All of my cars have been bought new, too.
2007 Nissan Altima bought new in Dec 2006.
Wife's 2008 Chrysler Crossfire bought new in Nov 2008.
My 2011 Mazda RX-8 bought new in 2011.
My wife's 2012 Fiat 500 Sport bought new in 2011.
My wife's 2012 Fiat 500 Abarth bought new in 2012.
My 2014 Mazda CX-5 bought new in 2013.
My 2015 Porsche Cayman that was custom ordered, and bought new in 2015.
My 2021 Alfa Romeo Giulia bought new in 2021.
My 2022 Alfa Romeo Stelvio bought new in 2022.
Hell, I could even add a few motorcycles bought new in that time frame where I'm bought oil at Walmart for them.
I'm pretty sure there are plenty of other BITOG members who have bought oil at Walmart for their new cars.