Transmission Leak

[AZ_Avalon]

1999 Avalon XLS with less than 100k miles.

It's leaking tranny fluid from the top of the transmission.

Not quite under the end of the starter on the tranny is some kind of button like plug. There is a cast in raised "C" approx the size of a silver dollar around it. The plug seems to be pressed in and does not appear to have a slot or opening on top-it's smooth. I don't want to do anything until I know why it's there and maybe why it's now leaking.
My lovely Chilton manual has nothing on it.
Does anyone know what the hell it is and does (besides leak)?

Thanks in advance.

[AZ_Avalon]

Originally Posted by AZ_Avalon

1999 Avalon XLS with less than 100k miles.

It's leaking tranny fluid from the top of the transmission.

Not quite under the end of the starter on the tranny is some kind of button like plug. There is a cast in raised "C" approx the size of a silver dollar around it. The plug seems to be pressed in and does not appear to have a slot or opening on top-it's smooth. I don't want to do anything until I know why it's there and maybe why it's now leaking.
My lovely Chilton manual has nothing on it.
Does anyone know what the hell it is and does (besides leak)?

Thanks in advance.

Ok, I checked the fluid today after a long drive and found that the previous owner or the dealer grossly overfilled the tranny.
My new question is whether our trannys have a vent and if fluid coming out of it is normal? By normal I mean what is to be expected in such a situation. I'm hoping it's not a sign of significant damage. I'll get it corrected ASAP.