Get the rubber over metal gasket from the dealer for a 42RH or 42RE trans.
They seal really well and are reusable.
I know it's kind of a pain in the butt, but there is also a small metal plate that covers the output shaft bearing snap ring that is normally cork and leaks just under the trans mount.
These can look like a pan leak since it is so close to the pan.
(Just so you know it's there)
