tranny leak at the dipstick tube

We used to ALWAYS put just a thin film of silicone inside the tube hole on the trans before we put the tube in.
If you put it inside the dipstick tube hole instead of on the tube itself, you will never see it from the outside.
The vent is at the top of the pump behind the converter but that's not the problem if it only leaks after cooling down and sitting.
I could be that the tube has a crack in it as mentioned, because when it is parked a lot of the fluid runs back into the pan when parked and fills the pan with more fluid than when it's running.
Sitting lets the fluid in the converter drain back into the trans kinda (overfilling it) till the next startup and the trans pump fills the converter again.