I've got differential oil leaking around the drive shaft. It is a small leak that is spraying the oil from the shaft all over the gas tank and underbody. Not enough to even cause a stain on the driveway. I caught it while doing an oil change. I checked the shaft and there does not seem to be any play or looseness. Could this just be the seal or is it likely that I will need a new pinion bearing as well? How hard is this to tackle? I believe that you can replace the seal while on the vehicle but I'm not sure if there are special tools involved. Truck has 152k on it.

Thanks for the help.