Is there a oil sealant I can buy to stop a small oil leak from my back gasket? on 1998 Mercedes-Benz E320

The mech said he had to take the whole transmission out costing $1,500 to fix it. i've heard of sealants you can pour into you oil tank that will stop any leaks?

Asked by for the 1998 Mercedes-Benz E320
yes there are but they will only work as a temp fix if your lucky