2001 Mercedes Benz CLK320 Transmission

We have our car in for the routine service at a Mercedes specialty service center, but not at a mercedes dealer. The routine service for that milage is about $375. They are saying that the transmission needs service and it will be an add'l $250 for changing the fluids, plugs, etc. Are they trying to sell us add'l repairs or is that normal that the transmission would need service at that time? All other warranty and service cycles were done at the dealer, but we are out of warranty at this point. Thanks!