I noticed that there was fluid on my rear axle on the drivers side a few inches away from where the axle connects to the wheel.the brake line next to it isn't leaking and there are no seals close to it.Is it possible that there is a crack in the axle that will cause a leak.

It is possible that it cracked at the leaf pack. The only way to find out is to go down there, clean the area up and inspect it.

I checked it out and I think I see a small crack.How can this be fixed?

The cheap quick fix is to stop drill the crack and weld it up. The better solution is to get a used axle.

All you need is the housing. Try to find one with a broken axle shaft or gears then swap your parts over to the new housing. That will save you a few dollars. If you weren't on the east coast I would sell you my spare.