The best way I have found to discover a leak like this is the following procedure.
Thoroughly clean, clean and clean again the area, without starting the car or anything else that may start the leak up again.
I found a nice little kit with a green colored dye you add wherever you think the source is. Engine oil pan, auto trans, etc. The kit includes a little fluorescent light that really illuminates the dye, pretty clearly indicating the leak. I have used my kit several times over many years in different situations. Just an idea.. good luck.