One problem related to timing tensioner has been reported for the 2010 Mercedes Benz E350. The most recently reported issues are listed below.
Was told to replace the serpentine belt tensioner. Asked why the belt tensioner needs to be replaced was told that they give out and if you are driving it could cause an accident. This is before the replacement cycle for the belt (90k miles). So many people won't know this will happen creating accidents that could be avoided.