I find it strange that your VW even has a transfer case /forums/images/graemlins/histerical.gif
It would help if we knew what transfer case you have or even what year the vehicle is so we can guess. If it has a slip yoke output, it is normal for those to seep a little fluid past the seal during usage. You have to replace stuff fairly often to avoid this. If the front output or the rear fixed output is leaking, this can be fixed easily by draining the case, pulling the yoke and replacing the seal.
If it is leaking from a seam, you will likely have to take the case apart just a little to fix it, but your chances are good that it won't require removing the T-case from the vehicle.
So where is the leak?