I too have used Delo for about fifteen years now. It took my original 240D engine to 380,000 miles and has served well in everything on my place from 4Runner, to gas MB, to diesel MB, to Ford diesel tractor, to lawnmowers, etc.

That said, Shell Rotella T MUST have something going for it. If all of a sudden I could no longer get Delo, I would have no qualms whatsoever switching to Rotella. It does have the highest parafin content of any of the Universal grade oils, but if you're changing frequently, this will cause no problems, in fact it might even be better for the engine if changed frequently enough to prevent parafin build up. I think the parafin difference is probably only marginal anyway.

My $0.02,