Delvac 1 5W-40. A fuels/lubes chemist I used to work with when I was in Diesel engine engineering convinced me it is the best.
Just switched from Rotella T.
Am now driving 2000+ miles per month.
Plan to get oil analysis at around 8000 miles. If still OK, will go to 10k mile drain interval.

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Now you're suckin' Diesel!

'88 300SEL
'92 300D 2.5 Turbo
'96 Lincoln Town Car. The Jazzmobile.