I've replaced two on two different cars in 10+ years. There's got to be something else wrong making it fail. I've never touched it on my 300SD and I've driven it over 113,000 miles on the pedal that was in it when I got it....
Replaced it on my wife's 300E about 3.5 years ago, no issues since.
The key here is that I have a spare on the shelf, and everyone knows having a spare of a part wards off failure.  Its worked great for me so far with the amount of spare parts I have! 
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-diesel is not just a fuel, its a way of life- 
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)
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