Older 300E models burn oil?

Well, yes mine sure does. I have a question along these lines. I have 218K on mine('86) and it consumes about 2.5 to 3 qts. every 3000 miles. I have no problem adding oil between changes, however the plugs look pretty black and oily after 10K or so. Replacing the plugs is no big deal either.
So here is the question: If I am fine with just adding between changes, is the engine ok with it also? Am I damaging the oxygen sensor or catalytic converters?

Adding oil to the engine frequently keeps you "tuned in" to other problems that may arise under the hood. Am I seeing a silver lining when there is none?

-Blake