And concerning the leaky seal. Did you nick the seal when you refitted the transmission? It's easily done. Or sometimes you can knock the spring off the sealing lips which of course lets it leak.

Another thought is that the seal has been popped out by Neanderthal Man with a big jemmy and he's scored the seal housing, so the oil's seeping out round the edge. This can be fixed with some crafty use of Devcon if you don't want to go through the rigmarole of welding, machining etc.