I think that is close to right on here, except: Are you sure that is where your oil is going?
I found out that my real oil consumption with the '91 300E was the upper front engine cover.
We got it at 129k, it now has 200k and the more I use the oils you describe, the better the consumption is. At the worse, it was about a 1 qt in 1,200 miles. The best is at around 1 qt in 2,800 miles.
The plugs remain oil free which to me points to: the stem seals are not leaking, they must have been replaced prior to my purchase ? or maybe not?!
I was told by an old Porsche tech years ago that it is the valve guides and the seals that tell the true initial story of how well a car is taken care of. If you run it gently until it warms up (no hard driving or high revs) AND you change your oil and filter appropriately with your driving habits, you should have minimal guide and seal problems.
It is hard to say where this good advice insects guides and seals that should have been made better, but I thought I would pass it along.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)