For 28 years, the tranny in my old van has almost always leaked for various reasons. This week after doing the gasket job twice, with the 2464324AC gasket that never leaks, it still leaked.
Turns out it was the same problem. Fluid is leaking from the switch itself, not from where the switch threads into the tranny. I put the truck in the air, cleaned everything REAL good, got a mirror and a flashlight, and inspected everything every 30 minutes. Only with the mirror and flashlight could I see the fluid dripping slowly from the switch. If you don't inspect it every 10-20-30 minutes or whatever it'll make it's way to the pan edges or bolts and again you'll be fooled into thinking it's a pan leak. I should have learned my lesson the last time I did this. I don't know how many gasket changes I did over a number of years and it ALWAYS leaked. After going through a similar troubleshooting process, I found that the culprit was a shaft in the back of the trans that had a bad O-ring. I don't know how many hours I wasted on this and how many driveways I stained.
Now I'm gonna let it sit overnight with a rag to soak-up whatever drips from the switch. If everything else is dry in the morning then I finally nailed it.