2003 Mercedes Benz 350sdl navagation part

The only possible alternative would be the possiblity that there is a software update or patch that may correct the issue that the tech has either missed or forgotten about. MB is constantly releasing new updates for the Comand and Navigation processors on all models to fix software glitches and errors that can disable the units. Before you have them replace the unit just inquire to the service writer. This is an expensive repair and the service writer should be able to speak to the tech and give you a clear answer as to how current your comand and navigation software is or if this is even a software issue at all. Keep in mind however, from my dealership experience I saw a lot of navigation and Comand units replaced due to hard faults that could only be repaired by replacement of the unit.