There is a thread somehere on here about intermittent starting difficulties, which flummoxed many owners (and SRT6 Mechanics ) until it was traced to the Fuel Pump Relay courtesy of the MB Forum.

The contacts on the relay apparently become pitted and cause intermittent problems. Once replaced; those who had reported the problem said it went away. Could be the same issue here.

Worth a try as the relay is only a few bucks and it's an easy self-fit.