I have 58,000 on my '98 C43 AMG and no problems -- I suspect that the AMG single engineer hand assembly and (at least in the case of the C43) tuning refinements to the already proven and robust 4.3L V-8 are likely to give longevity better rather than worse than the already solid normal M-B engine. In any case, owner care and maintenance will be the most important determinant.

AMG wear items (e.g., brake pads and rotors) are expensive, but not an everyday affair.

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'98 C43 AMG
'88 420SEL
'93 190E Limited Edition (including factory Sportline package)