I replaced the tranny fluid in my wifes 00 C230 at 1500 miles than again a 30k miles. I really don't buy into any of the "lifetime fill" propoganda assoc. with the transmission.
It's a very simple process, although I didn't receive much support from techs here on this site for doing it myself. Reason is the fluid level is supposed to be checked at 80'C. I really didn't see a need to pay a dealer huge amounts of money when I felt comfortable doing it myself.
No, I don't know for sure if the level is "perfect" at exactly 80'C, but I do know it's very close, and with 43k miles on it so far I have no reason to believe that I did any damage to it by not having it at the "perfect" level.
I purchased the dip stick from Mercedes along with the fluid and filter. I think it cost around $50.00 for the fluid and filter.
One other note is that in 2000, the convertors don't have a drain plug. So the most you'll get out with a filter change is approx. 4 quarts.