Mechanic said that this happens on BMWs (and Mercedes too). He said that without positive crankcase ventilation, the oil will push through the weakest spot. He did not know of any fix that would help however, except for allowing the oil to reach it's running temp (around 180F he said), which means longer trips.

Incidentally I talked with my Kansas City BMW dealer (Baron) about covering the repair (my passengers side valve cover leaked suddenly). They would not cover it and they said that they had no knowledge of this being a problem (no TSB, no campaigns, etc.). I even showed them many of the posts from X5World on this issue, but to no avail.

The repair cost me $550 at local German specialists shop.