Lucas Oil seal up front tranny seal...

Just a footnote to this thread. Most additives that say they will "Stop Leaks" should be called "seal swellers". As Trailbeast mentioned they will affect all the rubber components in the transmission and not just the leaking seal. In my much younger days, I worked weekends at, how shall I say, a less than honest used car lot. We never had a leaking engine, transmission or rear end. After a session with the old steam jenny, brake fluid was added to the oil(s) and voila, no leaks at least while on our lot.
Sniff some of those stop leak products and you can smell the brake fluid in them.