I posted some time ago about a leak from my AT. The leak is still there but it's not constant or very serious. The tranny is NOT overfilled with ATF anymore but it's still leaking a little from "somewhere". (it's been overfilled since the rebuilt but never leaked until this summer, when i found out i asked the shop to drain it)

The weird thing is that i found the source of the leak today and guess where it is... the fluid is comming out from one of the openings on the top of the tranny - a little black mashroom looking thing.(under the PS rack) It is a vent/air hole for the AT. There are actually two of these vents there. The inner one is leaking some fluid when the car is moving at some speed.
Does anyone have any idea why is this happening??? How it may be possible the ATF to come out of this vent?
The fluid level today was still a little above the "max." mark (just a little) but i drained a little more and now the level is really between "max." and "min." when the car is hot.

Any suggestions/ideas? I'm lost. The AT functions very well and it was rebuilt only 20k miles ago. Car is Audi 100, non turbo 5 cyl.
Thanks for any help.

Dan, Sounds like the old differential seal problem. This seal goes bad allowing gearbox oil to leak into the tranny. The tranny gets overfilled, and leaks!!!

This is a serious problem, Gearbox oil will destroy an auto tranny. Have the fluid checked for contamination.

The mechanics at the shop checked the fluid and they said it's in good condition. I visually inspected the fluid too and it looks soo clean -like new, even though it has 20k miles on it.
Also, i guess i confused you a little....the tranny doesn't overfill by itself...it was overfilled since the first day after the rebuild. They just put too much fluid in it. Then, few month later - after i noticed the leak, they drained it a little but i guess they still left too much fluid in it. Since yesterday after a second draining, the level is finally between the marks.
It's not that the tranny keeps overfilling itself...it doesn't.(or at least this is how it looks so far) It is very strange why fluid starts escaping from the air vent on the top? Could there be an internal damage or it was just because the fluid was a little too much??? I really hope it's the second, but i can't be sure. That's why i asked here if anyone had simular experience and etc. ?
Thank you for your input!