I just switched my car over from the old type of Mobil 1 Synthetic Trans fluid to the Valvoline Synthetic Dexron VI stuff....and it made a significant difference! It runs smoother, shifts firmer, and my looongtime iffy 3-4 shift is now firm!!!! I couldn't believe it! 60k with a weak 3-4 shift and now its firm...awesome. The stuff is only $4.59 a qt too....I got it during napa's 50% of day so I did a whole trans fluid/filter change for about $34! I do mine once a year regardless of mileage. All of our cars are now on the Valvoline Dex VI, and they all shift great....the other cars have been running it almost a year now. Highly Recommend it!

As for engine oil, I've found the Rotella Syn 5w40 to be a good product. And its cost effective on a 4k change interval.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)