I have resigned myself to changing a plug or two every year or so. Seems they never fail in the summer.....

If I was paying the dealer or another mechanic I would reconsider my perspective. I find the job tedious and irritating because of the intake manifold, but not difficult, complex or more of a risk.

The gasket is metal. You can inspect it and see if it is damaged or not. Mine look about the same when they come out as when they went in. So one has been back in twice.

The choice is just that, a choice. Just did a single plug, number 3 I believe, about a month ago. A couple have now been in for a few years. Most are less than three years old. But my choice is not about the cost of a gasket or the plugs, primarily. For the most part it is about leaving the things alone until breaking one off happens because it was not functional and I had to replace it. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)