Why has my Mercedes-Benz B150's gearbox failed at four years old?

I purchased a Mercedes-Benz B150 automatic new just over four years ago. I currently have 91,000 miles driven. It is serviced at six-month intervals by a Mercedes-Benz dealership. Following a recent service, on taking car back I noticed a strange metallic (slight knocking) noise, seemingly from the passenger underside. At the dealership, the diagnostic technician's opinion was the gearbox needed to be replaced. I am told that to replace the gearbox (including labour) will cost circa £4000. Asking for possible causes, nobody within Mercedes-Benz can give me any plausible reason for the failure. My position is to part with circa £4000 without a glimmer of observation as to the root cause of the problem. This I find most odd. Any thoughts John?

Asked on 12 September 2010 by eggo

Answered by Honest John
Yes, the CVTs on A-Class and B-Class models are starting to fail in pretty much the same way as they have been on Ford C-Max 1.6TDCI CVTs. But in the Mercedes-Benz vehicles, the boxes seem to last two to three times as long. The failure could be due to the owner's failure to replace the special fluid in the box, which needs to be done every two years.
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