Is this what you see?
Usually what you'll see is the dust seal lip 'tumbling' around the axle shaft.. The dust seals just help keep debris front entering the axle tubes.. The differential has inboard seals (installed from inside axle housing) to keep the lube in, and trash out.. On the older trucks, you may have also seen the larger outer axle/hub seal with a large ring tumbling as well.. Neither of them were/are a huge concern, but when the axle dust seal fails it can let trash collect in the axle tubes.. Generally the more the 4x4 is used, the faster you can fail a dust seal since the collection of dirt and dust and the friction/heat of the spinning seal against the axle tube face will cause the thinner 'bellows area' of the seal to crack and fail.. You could cut both the seal lip piece and the remaining portion of the dust seal off and fabricate a split end type repair seal.. Or, pull the axles and replace the dust seals.. Problem with removing the axles is they slide/drag on the tube interior, and if the tubes aren't cleaned out before install, you can collect debris on the pinch area of the axles where is seals into the inner axle seals and could create a leak.. If you use your 4x4 in a lot of mud and/or water a seal replacment or a seal of sorts fashioned/fabricated to keep the exposure to a minimum may help with the inner seal life..