97 sierra transfer case leak

Noticed some spots of fluid under my truck today. Crawled under it and found that it is coming from the transfer case where the front shaft comes out. Is there a seal there that can be replaced and how hard is it to replace. If not, what has to be done?

There is a seal but on my 90 K1500, it was leaking thru the shaft splines. I ended up pulling the tcase and replacing the chain and all the seals. I then used thread sealant on the front output shaft to prevent it from leaking again. That was a year ago and no leaks since.

You can see a diagram of your tcase here: http://www.rsgear.com/transfer.asp

//2000CAYukon