here in the states, a lubricity additive popular with Ford diesel truck enthusiasts is Opti-Lube XPD. As I recall, there were some fairly sophisticated technical tests/comparisons done. I used it, seemed to smooth performance and increase mpg a little.

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2006 X5 3.0 6-spd w/Evo UUC ssk
sport/premium pkgs
born Valentine's Day, 2006.