My 1980 300SD developed a major oil leak while on a trip yesterday. The leak forced me to turn the car around and head for home. During about 300 miles I had to add a GALLON of oil. Prior to the trip the car had absolutely no fluid leaks of any kind and required only a small amount of oil be added every couple of weeks. This was our first out of town trip in the car.

I discovered the oil useage and leak when stoping for fuel. The entire back end of the car was covered with oil spots and the oil dipstick barely registered any oil. I added two quarts of oil which brought it back up to close to the full mark. Another thing I noticed was that the oil pressure gage needle would vibrate and make a noise when the engine was at idle. The gage needle still stays at max once you step on the "gas".

The only thing that was different on this outing was driving at interstate speed for a sustained period of time, around 70-75 miles per hour. This car is normally driven by my wife on short local trips around town.

Now for the specifics of the "leak". During the trip oil was dripping at the very back bottom of the engine. No evidence of any leaks on either side of the engine. The leak appears only to happen when the engine is running. Parked in the driveway I see only a couple of drops on the ground and that could be left over from the trip.

Could this be a leaking rear main seal? A MBZ machanic told me it is rare to see a leak at the rear main, especially with only 193,000 miles on the car. Or since the leak appeared while at sustained highway speed could it be coming from the turbo?

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• 2001 E320