O'Reilly auto parts has Turbo Diesel Truck 5w-40, but not 15w. Flying J truck stops have Delvac 1. Spare yourself the hassle and just use Rotella synthetic. It's a 5k oil, pretty good soot protection, diesel rated. My car ran great on it. It's what I use when I can't find Mobil 1.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)