That seal keeps crap from the outside getting in, so long as it hasn't shrunk (and I can't see why it would have) don't replace it. On the other hand, if you plan on keeping that tranny for another 8 years or 150,000 miles I'd get new ones.
Just make sure there aren't any rough spots or rusty spots on your axles when you pop them in there. Use 600grit sandpaper to remove any of those spots if they exist. Then put some light oil on the shaft that will contact that seal, unless you go with new seals, then leave the shaft dry so the seal has a chance to break-in properly.
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"You have to know the truth, and seek the truth, and the truth will set you free."
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Yep, one seal for each axle. Personally, I'd replace them both while the tranny is out, but it isn't terrible to replace with the tranny in, other than re-pulling the axles.
You could replace them now, or you could chance it and not have to replace them or you'll have to replace them while in the car.
If you have a bad axle laying around, you can cut off part of the part that sticks into the tranny with the splines and use it as an axle seal driver. I have one and have used it a few times.