Marcos Maniacs

I wonder if anyone has experienced this problem. I have a 1970 Marcos
and I have a never-ending transmission leak. Initially, I brought it 
to a transmission shop and they did a complete reseal. I parked it in 
my garage, and a few weeks later I went to use it and there was a 
huge puddle of transmission oil on my floor. I brought it back to the 
transmissiom shop and they said it was the transmission oil pan 
gasket, they replaced it and I parked it in my garage and the same 
problem occured.
Since then I had the car at 2 other shops, and they both found the 
same problem and tried to correct it to no avail(they used all types 
of gasket materials). The last shop even replaced the transmission 
oil pan and it still is leaking. 

Note: It always seems to leak after the vehicle has been sitting for 
a while.

Any help will greatly be appreciated.

Thank you.
Michael