I rebuilt the vacuum pump on my 1980 300D about a year ago, so the oil in my air cleaner isn't from that. The only other place it could be from is from the black hose that comes from the valve cover (I know it's from there). But why? I have ~140,000 miles on it, and the car starts and runs fine. Except that I have horrible fuel mileage (e.g.- ~14 mpg), and it consumes tons of oil.

I'm guessing that I have horrible fuel mileage and lots of oil consumption because it all goes into the air cleaner. Any time I put a new filter in, soon after it becomes soaked in black oil, so I guess I can't expect to have good mileage. Someone told me to try replacing the valve cover gasket and the hose from the valve cover to the air cleaner. Do you guys think that would cut it? Any other possible fixes/solutions, for not only this problem, but also related to excessive fuel and oil consumption?