My 99 ML320 has been AOK up to 68K ... cannot complain about anything!
My 68 230S is such a basic car that I can't think of anything to really be concerned with; just got it and performing some (mostly cosmetic interior )refurbishments on it.
My 89 420SEL is in mint condition, but I am going to check the chain and guides shortly and probably replace the guides. I don't like all the vac lines on the 420, but they are not as big a tangle as they are on the 450SEL, which I just sold (really difficult to find and trace them all on the 450).

Overall, I am basically happy with the three Mercedes I have; no heavy complaints!

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Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)