Here's the guide I am using:

My attempt at replacing the transmission plug. - Benzworld.org - Mercedes-Benz Discussion Forum

Seems it is hidden behind a shield. A few posts down you can see his photos of what happens when the seal breaks and the fluid works its way up to the module. Looks messy!

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k