I found out today there are two sending units in series as the tank is called a straddle tank and has two separate compartments. They changed one ( that's my third) and I was told they (the sending units) have trouble working with our (American) gas. They're designed to work in Europe. There must be more of you than Dts.
I don't think the issue is US vs European gas, though it's possible that alcohol content in some US gas may be a problem. MB has a service bulletin, which came out last October, to replace fuel pump assemblies on C-class cars. Apparently the pump manufacturer (Siemens??) had a quality or materials compatibility problem with their first try at the fuel pump design. My C-240 pump failed intermittently at 6,000 miles last year. Since the pump was replaced with the new design part, it has been trouble-free, now at 21,000 miles. By the way - both sections of the pump (one side transfers fuel from left tank to right tank, and the other side delivers fuel to the engine) run off a single electric motor. The second part of the two-piece pump assembly is the fuel pressure regulator/fuel filter assembly.
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