Bill if its certified they will look after ya ,the seals are reasonable I have an account with GM ,ive done my own tranny on my last truck and one in a buddys,ive also totally rebuild a few transfer cases the transfer cases are very simply ,pull the drive shafts ,block up the trans ,pull the transfer case out ,the shift forks and chains went in the ones I fixed ,the only problem doing it yourself is getting covered in tranny fluid