Normally, a 2wd rear seal is very easy, but you're saying it's 4wd and leaking into the transfer case? If I remember correctly, the 4wd tranny does not have a rear seal. It bolts to the transfer case and the transfer case front seal must be leaking. Pulling the transfer case is not too bad of a job, they're light enough I don't even use a jack. I really don't remember what the front seal looks like, but I don't imagine it's hard to replace.