The fuel gauge sender in my mom's 97 E320 had to be replaced under warranty.
The fuel gauge in my 97 C280 occasionally gives the wrong indication, but works most of the time, I strongly believe that the problem is with the senders (two of them in the tank). I'm not too worried, though. When it does act up, usually once per tank of gas when the tank is around half full, it dances around and gives wrong indications for no more than 30 seconds. Although it has not done so in about a month.
I agree with you that there must be some type of common problem with them. When I called the dealer to get a price quote, they said they have plenty of them in stock, as if it such a common repair that they know to keep a stock of them.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record