Transmission should be serviced every 50K or so using the proper approved fluids. Your car has a torque converter with a drain plug, so that should be drained too. That way you will get nearly all of the old fluid out. Look at the list of items that need to be done at the A/B services and do them. There are also some time related items like coolant every three years (again using the proper coolant), brakes every two years, etc. A search ought to bring up those lists and it is in your owners manual packet too.

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles