IMO the best course of action is to assure that all casing bolts are tight...then monitor the fluid level regularly.
Verify that it is transmission fluid by having you (or your mechanic) clean the surrounding areas, then follow up in a week or two to see where exactly the leak is coming from. (From the picture, it seems to me that the leak is higher up on the drivetrain.)
If the drop or two every 6 months bothers you, put a pan under the car when parked. (Or a piece of corrugated cardboard, LOL)
That is a good idea. I just wanted to know where it leaks because the transmission case seems bone dry. The car has only 40k miles. Engine is good. But some age related issues seem to pop up here and there.
If you could sample the drip & then compare it to engine oil or tranny fluid. Engine oil & tranny fluid also has their own distinct smell. Was anything done before this happened? Have you checked the valve cover gasket? Or it could be that who did the oil change spilled some on the engine.