Leaking 4 wheel drive transmission

By four wheel drive transmission, you mean transfer case that has the front and rear drivelines going to it. The possible leak sources for this box are front output shaft seal, rear output shaft seal/bushing, where the case splits, possible cracked case where the fill/drain plugs have been overtorqued, or the transfer case input shaft seal could be allowing transmission fluid past it and it is overfull. If the latter is the case, the transmission fluid level could be low as an indication.