i wouldnt suggest messing with an auto transmision unless you have enough experience, get some bad trannies from the junkyard and try with those first, learn how to dissassemble it and rea ssemble it until you can do it blindfolded, also get the service manual and read it cover to cover before doing anything...
a transfer case is easy for almost any one with opposible thumbs, you can use almost any RTV as long as it comes froma good brand