I can't believe you were quoted $550 to change the plugs on an ML!!??
I have done the plugs on two ML's recently and it is not a really tough job if you use the right tools. The 12 plugs cost $50 retail basically and any good mechanic you want to use should charge no more than one hour's labor or so to do the whole job, if they are used to working on the ML. Dealer's simply rip people off on brake jobs and spark plug replacement, etc. etc.

If you don't want to tackle the job yourself, find a couple of good local mechs and get some quotes; you will save a lot of money and still have it done properly.

(If you want to do it yourself or with a friend, read the excellent posts in this forum regarding changing plugs on the ML first.)

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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)