My friend has a 2002 C230. Recently he brought it to the shop and they replaced some harness of the transmission. A few days after the car will not shift out of 1st gear. It will also go into reverse. As this is a sealed transmission the oil level cannot be checked. I am not sure if it is electrical or if the oil should be changed, or topped off. The car has 95k on it.

Tranny tube can be accessed, and fluid checked with a "shop tool" which can be fonund on the Fast Lane site here at Peach Parts:
http://catalog.peachparts.com/ShopByVehicle.epc?q=2002-Mercedes--Benz-C--30-Transmission&yearid=2002%40%402002&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6328%3AED%7C744%3AMBC%7C1627%40%40C230&catid=241185%40%40Transmission&subcatid=241272@@AT+Dipstick&mode=PD

The Plug Adapter is a common failure on the 722.6 transmission, and when it leaks fluid can leach up the wiring harness to the AT Controller. Plug adapter is an cheap and easy swap, but if you don't do it soon enough the fluid may trash the controller (AT controller is located under the passenger foot box) Might be able to salvage with cleaning--if it's that far there may be not much to lose in trying. Do a search on here, there's some good threads on the topic.

Good luck.

__________________
Earl McLain
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)