Don't use silicone on threads. Instead use Oatey white pipe sealant with Teflon.
Also keep in mind that alum trans pans, and all other aluminum gravity cast parts can be porous. I've seen it in intake manifolds, trans pans and other gravity cast parts.
Permanent mold, pressureized molded parts such as timing covers, etc. rarely have that issue.
I've had trans cases that weeped fluid too
To find those not so easy leaks, clean the area with rags and brake cleaner, then spray the area with spray on flour, used on baking pans for cooking. As soon as it leaks, it's easy to see from where it's coming. Dry spray on armpit deoderant works almost as well.
TIMINATOR