ECM/ECU completely shot????

I have a 1995 Mercedes S420. The check engine light is on. The car is running fine. The dealer claims (after charging $80 to check it) that the whole ECM is bad and needs to be replaced because it is not reading the information coming from the injection system. They called it a "hard fail", I thought the car would be in limp mode if there was any hard fail. Anyone got any advice on this? The part alone is $2100 at the dealership, and I have a hard time accepting that its bad to start with. Thanks, pardon me if I broke any rules of etiquette, I am brand new to this forum.

opnwyder