The front axles have a seal inside the axle tube that eventually needs replacing. The rear axle relies on the outer seal just behind the axle shaft flange to keep oil out of the wheel bearings. If you have leaky inner wheel seals, (they are the same front and rear) this will go a long way towards sucking gear oil out of the axle assemblies. Wheel bearing grease off of the shelf at Walmart works just fine. On a truck that has seen years of unknown service, pulling everything down to the bare front axle balls is best. There is a tapered roller bearing on the bottom and a tapered brass cone on the top. By the way, the reason for the top being brass(you can also use the same style tapered roller bearing on the top), is that the load on the knuckle is from the bottom, the top has only radial loads. To get the best strength and longest wear, you have to make sure you have proper pre-load on these knuckle setups. Too loose and and you can break a knuckle. Too much preload and you wear everything out but get strong arms in the process. Pulling the axle tube seal on the front axle can be a bear. Working on these old trucks is so much fun. Best of luck.
