I've had problems getting the rubber gasket sealing on the pan. I decided to try the cork gasket. Of course the installation was messy, but easy. The cork is far superior to the rubber one. Haven't had one problem with a leak since installation. Highly recommended.
I had rebuilt my tranny and had installed 2 different types of rubber gasket and both leaked fluid. I installed the cork gasket, test it and no more leaks. So far so good A+++++