When I bought the parts from the dealer, the Oil Separator of course came with the "updated design". Basically foam insulation around the Oil Separator (which I am not convinced is the solution but whatever...).

Well, during installation, it was virtually impossible to squeeze the Oil Separator in place (I did it with the manifold in place, only the OFH was out), so I ended up removing the insulation foam, then it was a breeze to slide the Oil Separator in place, then connected the vacuum tubes to the Oil Separator.

Whatever it is, I personally don't think the insulation helps much. What matter is: avoid short trips as much as possible.

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT