My 2004 C230 will not shift out of first gear

Make sure you used the right fluid and that the level is correct , were there any metal bits in the fluid when you changed it ? Was there a magnet in the pan ? Did the replacement parts match up perfect ?Was there any O-ring , spring or anything that came out when you dropped the pan ? If it doesn't begin to function normal take it to a good tranny shop .

The likely cause of your problems is that twenty year old transmission; occurrence of the leak could be just coincidental. If the car has a couple hundred thousand miles on it, it might be lack of proper maintenance, and any Mercedes requires way better care than the ordinary car. You now need to have a Mercedes transmission mechanic review the problem.