Transmission Fluid Leak

I own a 2004 Chevy 2500 HD Silverado With 40,000 Miles on it. I had a remanufac. Transfer case from GM installed in by a transmission shop. I have put 1500 miles on it since the work has been done. I have noticed a small leak of trany fluid where the transfer case bolts to transmission. I can see a new gasket and what looks like some type of gasket sealer. The truck is still under my 90 day Warr. When I called the transmission place up and told them and then asked them if they had any ideas they said maybe a bad gasket. Now that I brought the truck back I am being told there is a seal in trany that is leaking. I asked why is there a gasket and gasket sealant between the trany and transfer case I was told that is to keep dirt and water out. My question is, Is there trany fluid inside where the two bolt together. And does it belong there? And the gasket and sealant is there to keep the fluid in and not dirt and water out. Thank You