I have 06 EB v8 with 111k miles (including towing and plowing), and my rear left went bad at 75 K, a shop replaced it and it went bad again in 10 k miles. They replaced it again under warranty, and it's OK so far. My right front bearing went bad at 99 k miles, but it was not really the bearing but ABS sensor which is inside, so I had to replace the whole thing. I bought the replacement on ebay for 120 bucks, looked nice, but it broke before I even put the car down, the wheel was wibbling all over. They send me a replacement (both made in China), and it was the same case. I bought a new one from Ford for 330 and it was it. I guess what I am saying, get the OEM parts if you can. On your question, 50k is kind of early, but it may happen. The front you can do yourself if you have tools.