Is your car a 1998 or latter?
the sealed box conundrum.
A guess you have a MB 722.6 trans, it takes special fluid that is pricey, and that is the only fluid period, a special dip stick tool to read fluid level, and a filler tube cap.
But I have the same trans, I researched and change the fluid every fifty thousand miles in mine.
Do a search on this site, cause I think Mercedes made a few improvements for when you change fluid, like a special magnet in the pan to collect debris, and a few other items that may not be all that important to worry about, but educate yourself by searching the 722.6 transmission.
Don't you sleep, it's like three o'clock in the morning on the isle.