Well, my engine only has 140k miles on it...and it doesn't do the tapping all the time. I guess I'll try some solvents...would an oil for "high mileage engines" like Valvoline Maxlife be a good idea?

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