There is a plug located on the transmission pan and one located on the torque converter. I replaced the plug crush rings when I replaced the trans fluid on my 98 E320.
Also be sure that the transmission fluid is at operating temperature when checking the fluid. You will need to replace the locking pin on the trans dip stick cover since the locking pin must be broken to remove the trans dip stick cover.
Do a search on 722.6 trans to gather more info.
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles