Investigate as to why this seal is leaking. Is there any movement other than rotation in the pinion? Is the seal surface on the companion flange grooved/damaged? It is really not that big of a deal to replace the seal. Unbolt the driveshaft at the rear companion flange, remove the pinion nut, remove the seal, look at everything, install new seal if you do not find any funny stuff going on, retourque the pinion nut to factory spec outlined in the manual(sorry, forgot that one off the top of my head somewhere around 125ft lbs I think)
if you did not get a new pinion nut, use some blue lock tite, and try to re-stake the nut if you can, install your driveshaft bolts( I use blue locktite on those also), verify the fluid level in the diff, and you are done. I usually change out the rear diff oil when I change out the pinion seal, as to see the amount of metal in there, oil is cheap.