I'm helping my brother fix his truck ASAP. I've already searched around. 2011 F150 Platinum, 3.5, 82k. Full Livernois kit on it, truck is a beast. Stock wheels/tires/suspension. His driver side axle was starting to click and bind up so he bought a new half shaft from NAPA. He installed it and somehow the seal in the diff came out during his install and he didn't realize it. He noticed it checking for leaks his test drive. He removed everything but couldn't get the seal back in. He calls me, I drive out and install the seal. Put everything back together, we drive it for 20 minutes, runs great. Next day, 30 minutes into his work commute he starts to get a vibration from the driverside front, he can feel it in the steering wheel. I suggest returning the NAPA part and getting a new one from Ford. He did that, and installed it. Same problem, 20-30 minutes into driving he starts to get a vibration that you can feel in the steering wheel. I told him to feel around and see if anything is hot. He says nothing is hot. I'm thinking maybe he lost more fluid than he thinks, the stuff that did leak out didn't even look like diff fluid, it was more of a white/yellow lube. Any thoughts?