Dear Friends - I have a problem and three different garages are each giving me a different solution. My 560 SEC (1988) suddenly died at a traffic light. I restarted and all was well. The next day it wouldn't start at all. Neither the AA nor my local garage (chief mechanic away) could start it. It was towed to MB Hampstead. THey started it by tapping then changing the fuel pumps and fuel filter. Two days later it happened again, near Stratford. But it restarted at once. An MB main dealer in Stratford told me on the phone he doubted it was the pumps - more likely the relay.
MB London - when I told them I had run the car for 18 miles on the reserve tank, said dirt had got in, without a doubt and told me to put in injector cleaner and run it. Today - three days later with a full tank - it died again. But again immediately restarted. MY local garage said it's not dirt, it would have sputtered and chugged, not just died. MB London say drive it till the cleaner gets to the injector, after that all will be well.