If you are talking about the Pan Gasket, here is what you do. Pick up a Transmission Filter Kit from NAPA, Autzone etc along with 6 quarts of Trans Fluid. The Filter kit comes with a new filter and a gasket. Remove the pan bolts, have a larget catch pan to catch the fluid, because there is no drain plug. Once the pan is dropped replace the filter and re-install the pan with the new gasket. Put 3-4 quarts of fluid back in transmission through the dip stick in the engine compartment "before you start the engine". Start the engine and let it idle and the trans fluid get warm. Add fluid until you reach the full mark for hot fluid. Be careful not to get to much because there is no way to drain it except by dropping the pan again.
Remove transmission oil pan for acces to filter Replace fluid, filter, and gasket
Remove the transmission oil pan for access to filter Replace fluid, filter and gasket
Remove the transmission oil pan for access to filter. Replace filter, fluid, and gasket.
Remove transmission oil pan Replace fluid, filter, and gasket
A transmission fluid leak means that the plug may need to be replace, or the seal or gasket may need to be replace. As it could be caused by a work seal, or gasket, or a loose plug.
Replace the gasket on the transmission pan and insect the seals on the transmission where your driveshafts come out
Remove transmission oil pan for access to filter. Replace pan gasket, fluid and filter
You will need to drop the transmission pan and replace the gasket. While you're at it, replace the filter and clean the pan.
Drop the lower transmission pan Clean pan Replace filter and gasket
You need to check the transmission gasket between the transmission pan and the body. If it's leaking you have to replace it.
That is a scary situation. The best, and cheapest, thing you can do is immediately replace the gasket. You can keep driving it with a slow leak, but you will have to keep putting transmission fluid in it. Which will cost you more in the long run. If you replace that gasket now, You won't have to worry about constantly re-filling the transmission fluid.
Drop the pan, replace the filter and gasket, replace the pan and add transmission fluid.