I don't really see how you can predict something like that. Mercedes reliability has been all over the place the past 10 years, but trending upward again. The next CPO car I buy may well be a 2006 S350. I like it because it's the simplest of the S-classes (w220) and the last of that body. I'd say you'll end up with the most reliable w220 in the series, fwiw.

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL