for the details on crankcase ventilation on the 104.99x engine, see page 4 of this PDF, http://new.freescruz.com/.priv/W124/w124CD1/Program/Engine/104/01-0400.pdf
its fairly complicated and clever.
And It's very effective at keeping the engine clean as can be seen in my M104.995's like-new valve train with 228k miles on it.
Of course the previous owners' maintenance schedule and choice of oil and filter may have something to do with it as well.
PS. Here's another interesting article on the M104 crankcase ventilation and vacuum although it applies to the W210 body so the idle control valve and PCV valve doesn't apply. Also, there is no need to use an adhesive to glue the VC gasket into place.
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