Mercedes-Benz upgraded the valve guide seals on M103 engines to viton seals during the 1988 model year. In April of 1989, they updraged the valve guides themselves.
Vehicles with upgraded seals alone may go a little longer before oil consumption gets really bad, but not much longer. It is sort of like putting a Band Aid on a really big cut.
Vehicles that have both upgraded seals AND guides seem to go ALOT longer before needing a full valve job. At our shop the average mileage that vehicles with the upgraded seals and guides seem to go before needing a full valve job is 150,000-200,000 miles. On many of these vehicles, we replace seals alone the first time the vehicle starts to use some oil (often around 80,000-100,000 miles), and we find that the updated guides usually have very little play at this type of mileage.
On vehicles with the older valve guides, we often do full valve jobs between 80,000 and 110,000 miles.
We also find on many vehicles like yours that are old in years but low in mileage, that the valve guide seals tend to dry up due to age.
I would replace your valve guide seals only. While you are in there, test the guides for play. I would be surprised if they have any at all at 67,000 miles.
Let me know what you find.