It's always the peripheral stuff on a Benz that can cost you the earth. If everything electric works (climate control, seats, windows, etc.), then it is probably OK to buy it. Routine maintenance parts should never be a reason to not buy a car. I know you'll like it. My wife's C280 has almost 300,000km on it now and it still behaves and drives as new. It has been across the country twice with no hassles. We are considering giving it to my parents and getting her a smaller, more fuel-efficient car for her long commute. If my >500,000km 190e which still consumed no oil when I sold it is any indication, my parents will get many years yet out of the C280.

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'96 C280 (gone)
'97 C36
'05 C230k