The T6 is probably fine for your car. My original post was somewhat tongue and cheek. If you type "synthetic oil" into the search bar, you'll find that there are different grades of synthetic oil, and T6 is not the highest. I'm pretty sure that Mobil1 got downgraded recently and that Amsoil is considered the best.

I bought the Castrol diesel oil a while back because it was on sale, and have been pleasantly surprised at how well it has held up.

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'81 300SD