I noticed my car was harder to push backwards than it had been, at the same time had a small differential leak. I took the driveshaft out and found the pinion nut just hand tight. I put a new nut on, with loctite, around 250 ftlbs, and it was then back to normal in terms of how hard it is to push, and no more leak. I also engraved the pinion and nut so that I can look in and see that the nut is where it was when torqued in.