Maybe I took things too easy but I have no degree in rocket science so I filled up ½ liter of oil whenever the level was below the bottom indicator. Could have been all wrong but my M3W survived several years and plenty of miles with that philosophy.
As far as I remember never needed more than a liter per year, milage 3 - 5000km/year.

Hannes
once: Green M3W; 2013
now: Red 4/4 Sport; 2011
and some practical cars for use in real life