I just got a call back from the mechanic...he said both fuel pumps are tired. They are making a lot of noise, and the fuel pressure drops by almost 40psi when the misfiring occurs. Repair estimate $750. O_O

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles