Just out of curiosity, are you testing it with water before or after bolting the impellers completely down? I ran into this problem replacing the tub seal in my GU940. I would seat the seal perfectly, had coated it with dish soap and the whole bit, and as soon as I put a cup of water in, it would dribble out straight over the motor. It wasn't until I realized that the impeller bolt pushes the drain impellers seal against the tub seal that I didn't have a drop leak out.
You may have this under wraps already, and if so I'm not sure about why it would be leaking with the new seal, but I figured I'd just throw that out there in case it was any help at all.