Ditto mbshop. I see you've been doing this for 30 yrs. Thanks for taking time to help the diyer community.
Havoline Dexron-III changed every 15,000 miles + new Mann filter and pan gasket that you do not want to over-tighten.
Synthetic for new cars....maybe??
Older ones....work just fine on the older stuff and frequent changes, be it oil, dexron, 80w-90, etc.