Well consider this,-
We bought 2 e220 cdi's brand new in 2000 and myself and my partner decided to conduct a (not very scientific) test......
W934 was serviced according to Merc's specs with jolly old Shell helix
and lasted 220K then died.
W935 on the other hand was retired earlier this year having been around
the planet 18 times (450K). We only got rid of it because it's no good
running a 7 year old vehicle at a Chauffeur Co.
The only difference between the 2 was W935 was run exclusively on
Mobil 1 and topped up with slick 50 every 50k.