Simply said, synthetic motor oils are far superior lubricants by any measure compared to petroleum oils. One of the best synthetic properties is resistance to heat. Diesels produce higher internal temperatures than gassers.

There is a persistent myth that using synthetic oil in an old engine will produce leaks. That may have been true 30 years ago but modern synthetics have no such effect. Basically, if your engine did not leak with petroleum oil, it will not leak with synthetic. I use synthetic in my 35yo 300CD (324k miles), my 2008 BluTek E320 (80k miles), my 97 Dodge (170k miles), outboard motor, weedwacker, everything.

My personal choice is AMSOIL but there are many fine synthetic oils out there. I use 15w-40 in the old Benz, 5w-30 in the newer one and 10w-30 in the Dodge.

I'm almost certain that others will post more scientific responses but that is mine and I'm sticking to it.