Transmission leak

There are a number of things that can be leaking from that area but the most likely cause of this would be a speed sensor.

So, I am attaching the info that shows the views of this side of the unit so that you can have a better idea what is up there.

What I would suggest is we use oil dye to trace the leak. If you haven't done it in a while, I would service the unit and when you put new fluid in it, add a little bottle of oil dye and then run the vehicle. Once you see the leak you will be able to use a light to illuminate the dye and see just where it is coming from. You may need to use a mirror to see on top of the pan.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Take a look at the diagrams below and let me know what questions you have. I put a red arrow where the starter is so that it will help orient you.