Where is the drainage nut for my 1998 GLE's auto trans? What type of fluid should I replace it with?

 

Just look under the car. The transmission drain plug is located right beneath the engine, and a little to the rear and left (driver's side) of the oil drain plug. The transmission drain plug is on a black square shaped pan.

Your transmission takes Dextron III (3) ATF. I use Redline synthetic D4 ATF in mine.