These sealed transmissions are expected to take you through the warranty period which is about 100K miles, after that it all becomes your responsibility as far as MB is concerned. I know many 210 cars, gas and diesel that have gone close to 200K with original transmissions untouched, but you never know. Most private shops will tell you to definitely change the transmission fiter/oil at 50K intervals as a preventive maintenance measure if you intend to keep the car, but if you have a high mileage and the thing has not been serviced, DO NOT TOUCH IT, keep on driving and hope for the best.
I have a E320 97, had the tranny oil&filter changed at 70K miles and plan on doing it again in about 40K miles.

Vahe
240D 77 350K