The repair is doable for a DIYer who is mechanically inclined and equipped with the proper tools. My biggest reason for reply is to urge you to clean the transfer case well before you do anything else. Have someone sit in the driver seat (Not in gear and parking brake on) and give the engine a couple thousand rpm's. While they are doing this look on the passenger side of the transfer case towards the front portion and see if you see fluid leaking out of an area you would not expect it to. Chevy has an engineering flaw where on some models the transfer case pump eventually breaks off a metal clip used as a shock absorber and scrapes a hole on the side of the transfer case. This just happend to me. I had leaking from both seals but when the seals were replaced there was still a leak. It was hard to tell where the leak was coming from because of all of the oil and dirt built up on transfer case. After cleaning off the entire case well, I had someone rev the engine a little bit and saw a steady drip coming from a tiny pin hole in the area I mentioned. I did some research on youtube and found lots of hits for this problem. Look for one in particular from "Truck U". This may not be your issue, but it seems to be very common.