I have a 96 320 with 168k miles, when I drive hard you can smell some fluid burning sometimes a little smoke. I have checked the fluid levels and they are bang on. There is no dripping from the car. If I don't get on it nothing, no smells or smoke.

 

I'll take a shot....valve cover gaskets.The reason you don't see any leaks is because of the airbox.

 

you have m104 engine which is known to leak from timing cover (front engine passenger side, look right above alternator). most likely the oil is touching hot exhaust parts and that's when you smell the oil burning and the white smoke. the leak is probably small so you don't see any oil on the floor, but probably have oil accumulating on belly pan. nothing to worry about, leak is external so as long as you have enough oil in your engine it's ok. if oil leak gets worse (can take years), then you might want to reseal the timing cover (couple hours easy job). also if you confirm you have a leak you might want to use dino oil instead of synthetic, since it will minimize the leak.