SW is offering a good suggestion of items to check.
The vent and drainback system on these engines are a problem. Once the engine starts a ittle blowby it turns into a mess.
There is one suggestion that I got when I was pusuing this, that you may want to check out.
There is a baffle inside the valve cover that as it came from the factory allows too much liquid into the breather hose once the engine starts making blowby. You can remove the valve cover and use five minute epoxy to seal all around the front portion of this baffle. Leave the rear most opening clear. My daughters car has much more oil usage than yours so this did not help much. But if you are at a quart in a thousand miles, this is definitely worth checking out.
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in