@VDC Right; we had a Chevy Impala that we drove to over 300,000 miles and it used a quart every 2000 miles or so over most of its life. It did not smoke and ran perfectly.
Oil is cheap and if the engine runs well I would not bother with trying to “fix” the oil consumption.
Rented a Matrix on holidays some time back. The owner’s manual stated that oil consumption of a quart every 750 MILES! or more was considered “normal”. With 0W20 oils that can be expected.
Given the age and mileage, it needs to be checked for gasket and seal leaks, PCV valve operation, and evidence of burning oil, like oil fouling on the spark plugs. If they haven’t been changed yet, you are past due for spark plugs, PCV valve, and a valve lash adjustment anyways.
As far as something like Marvel Mystery oil is concerned, I have an open mind. If the general consensus around here is that it or some other snake oil is worth trying, sure ! As yet, all this experience has not seen fit to endorse this wonder of wonders.
I don’t know anything about Marvel Mystery oil, but I’d worry about putting anything in the crankcase except what the manufacturer’s engineers recommends if the car sports variable valve timing. That actuating mechanisms for that function are sensitive to the oil parameters.