Hmm all of that sounds right. How about the after next time you drive it so it gets to full operating temps for over 20 or so minutes, wait till its cool again and check the smell of the oil off the dipstick before starting it.
A lot of cold (rich) starts in cold weather definitely contribute to gaseous oil.
From what you said, it doesn't seem to be using a lot of fuel....
How does it start warm? Hot?
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)