F-150 1993 transfer case hole

In checking out the dash board 4X4 light signal wire connection to the transfer case underneath my truck, I noticed a 1 to 2 inch diameter hole in the bottom of the transfer case and see a dark smooth surface through the hole. Should there be a hole this large in the bottom of the transfer case? Did a transfer case seal fall out? There is also a coat of oil over most of the outside bottom of the transfer case.
Thanks