Just had the MAF sensor replaced on my 99E300Turbodiesel at 48k. My tech suggested that the high failure rate for this item is partially due to the extended service interval (FSS) for the newer cars and he recommends a new air filter at a much shorter interval depending on driving conditions. In certain parts of Texas, that could mean twice a year due to the sand in the air. According to my tech, any dirt or sand that gets by the filter blasts the fine metal grid of the MAF, rendering it useless.
Also pretty useless is the FSS.