Fresh 383 rear main leak during install

I had to redo my 440 rearmain seal after rebuild. Now I have a fresh 383 4 speed and pretty sure the rearmain seal is leaking on it too . Very disappointing. If it's not leaking much you can run it and it might tighten up. Mine didn't on my 440. But I was able to keep engine in car (68 dart) and pull trans (727) and just install new seal and it never leaked agian. As we speak I am debating weather to try the same procedure with my 383 4 speed, or pull the engine to install new seal.