I have a power glide tranny. Over the winters since 1998 it has leaked 1 quart of tranny fluid every year. It is the only fluid this car leaks. I changed over to a neopreme gasket in 2005. It still leaks the same amount every year. Once the driving season starts it does not leak. This is a problem only over the winter storage season!
I know that when trannys sit over the winter the torque conveter leaks all its fluid back into the transmission causing it to be way overfull and then leak from every available oriface. Sometimes there are fixes for this and sometimes not I would talk to a good tranny shop and see what they say. But also the leak may not be the pan gasket it could be the dipstick o-ring or something even higher up on the case.
I had a similar problem with mine during the restoration, it would only happen after a week or so, turned out that once I pulled out the dipstick tube and applied a thin layer of RTV black around the o-ring and put it back in place. It has not leaked a drop since.
-- Edited by 69SSConv on Saturday 30th of April 2011 02:40:20 PM