Transmission fluid leak

We just purchased a 1998 ml320 a month ago. I noticed a fluid leak which I thought was an oil leak until i saw that the fluid was reddish in color. I can't find where to check the transmission fluid. Yesterday after sitting in traffic for a while I had stopped at a red light . when I went to go when it turned green my car sounded like it would not go into gear. I immediately pulled over and tried to check the fluids and from what I read in the owners manual , I can only take it to a dealership. Is this the case? I can't even find where I can add more fluid until I get it to a shop. I did let the transmission cool off and tried driving it to see if it did that again. It drove fine and I was able to get it home and it will sit till I can figure out what to do with it.
Does anyone know how to add transmission fluid to this car? How to check it? Or am I stuck bringing it to am expensive shop? I am doubting this purchase now.