leaking differential

[srvblues]

Well it was a beautiful day today so i decided to take my 1995 gt stang out on the town. I don't get to drive it often during the winters up here in Idaho. Anyway i drove it into town messed around and then drove back home. I come out later that afternoon and noticed oil leaking from the differential. got underneath to take a closer look and seen a trail of oil from the rear up to the yolk and it seemed to be coming from that area. the oil spot is not large and it is fresh. i know it has got to be fixed but what is the best approach.
i didn't think i drove it hard at all but she didn't like something i did.
i was planning on getting cold air induction kit and kat back exhaust this spring but since i have to work on the differential is there any other mods i can do while it is apart. Also just to fix the leak how much ballpark am i looking at?
She is a 1995 GT all stock and looking for a makeover... hee! hee! only 65,000 miles and in great shape except for the leak.
Thanks for your replies and keep the rubber burnin