I wonder if you don't have an oil pick up problem. It looks like the way the oil sloshes is important. Do you have the level up to the full line? If not it might be interesting to fill it up to see if things improve, however, I agree that the pan has to come off, but if the problem is with the oil pick up, it might not be too expensive. I'm thinking the pump may be sucking air with the oil sloshed away from the oil pump, like if the pick up tube has come partially loose. This is just a WAG because I don't know what your pump arrangement looks like.

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'97 E 300 D