I know Subaru "requiring" Synthetic oil changes have wiggle room in the O.M.
Hidden somewhere - purposefully, so dealers can up-sell their "Subaru Genuine Synthetic Oil" -
is the statement that the use of Conventional oils will provide adequate service
with no harm to the engine.
In my 2018 Outback owner's manual it says to fill it with full synthetic 0w20 and in the event of oil consumption you can top of with conventional 5w30 if one so chooses.
I have been looking into Castrol oils recently to decide on what to use in that 2018 Outback as well as a 2012 Hyundai Accent and 2004 Chevy Venture. I am thinking SP Edge High Mileage 0w20 for the Subie but can quite decide on which Castrol 5w30 to run in the Hyundai and Chevy.
Ultraclean and GTX High Mileage look good for the price BUT I could spend a few more bucks and get Magnatec BUT then again I could spend a few more bucks and get Edge High Mileage. What is really "worth it" if I am just looking to clean up two old, high mileage engines both with an OCI average of about 4000 miles?