My '97 C280 has 140,000 miles. Still original tranny and original headgasket with no leaks. The headgasket was a common weakness, but they haven't ALL needed to be replaced. I would check to see if it has been specifically reaplaced on that car. The updated headgasket had added metal inserts to help keep it in place.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record