2008 Tacoma 4x4 tranfer case leak

I have a 2008 Tacoma 4x4 with 4000 miles and at about 3000 miles hase developed a leak that seams to come out from the rear seal where the driveshaft connect. I have had it back 4 times to the dealer and they have replaced the seal then replaced the back end of the tranfer case and now the whole transfer case. but it still is leaking. they now have replaced the drive shaft and i have know clue why they would do that. Well after 200 miles it is once again leaking from the rear seal. Can anyone help me.