Does anyone have the a picture ML 320

The usual layout is: exhaust manifold, sensor 1, catalytic converter, sensor 2. So look for it IMMEDIATELY after CC. I would imagine MB hides it above the exhaust pipe. If you cannot see it, use your hand to feel it (of course, when the exhaust is cold).

I did replace the sensor 2 > Does anyone have a picture of the location of the oxygen sensors on a 1999

Use a OBD2 scanner and look at the value of the O2 sensor... Sensor 2 should be a slow moving... as long it is not zero, it is good.

It is most likely your MAF is bad rather than your O2 sensor.

For your information, O2 sensors should always be replaced in pair... not a single one.