Thanks for the info!
I just did a Google search for
transtar + 13615bx and it lead me to a pdf (atsubr4ax04.pdf) that has some nice exploded views of our 4EAT transmission. The company sells rebuild kits as well as individual parts.
Yes, according to the pdf, that is a gasket for the oil pan of the "1st design" of the 4EAT transmission.
Go grab the pdf if nothing else.
Dan