No, the leak was there before I switched to synthetic. I am going to see how 15W50 plays out as the winter draws nearer... I live near Toronto. I switched to the 15W50 on the recommendations of this forum.

In my other cars I am still using Castrol Syntec 5W50 which I have been using for more than 10 years, but didn't want to use that in the MB. The 5W50 has been perfectly fine in the winter and summer for the other cars.

The Mobil 1 15W50 cold pour point is -49F, so I imagine it's going to be fine for my uses (my car is in a garage overnight anyway, and that's when it gets coldest...). The 15W50 as discussed here many times seems to be pretty popular for our MB diesels.

Mobil 1 doesn't have a 5W40 or 15W40, and the 30 weight oils are no good for our use. So the options with that oil is 0W40 or 15W50, and the 15W50 has more praises than the 0W40 from what I've read here.

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1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)