Its not the fluids on the exhaust smell, and it is not the catalyst converter smell. I know what those odor smells like. catalyst fail has rotten egg smell and tranny fluids over heat has a different kind of burning smell. My car smell like burnt clutch, a very strong odor. I think the tranny slips a little seems like, but the car will still accelerate with speed. So I assume the slipping is not servre. Once again the odor comes on when, say you're going at 60mph and you want to pass someone so you floor the gas till you see 100mph on the speedo. At this time I start smelling the burning smell like burning clutch. If I ease on the gas at 60mph till I hit 130mph the odor is very slight. I can maintain speeds at 110mph without any odor. So the smell comes on with sudden acceleration. I will check the color of the fluids just to make sure. I have a 1997 S500 with 5 speed. the tranny should be a sealed one. supposely maintanence free. There is no odor at any time other than fast acceleration high insanely high speed which should be normal for these autobahn cars.