trans leaking again after rebuild

I've rebuilt quite a few Mopar autos. There is no way I could do it in under 4 hrs.I suppose a well seasoned builder might, if the trans was clean, and basically in good shape;so he would be doing just a reclutch. Shoot, I take over an hour in the VB alone. And sometimes it takes more than an hour just to clean it.
And once the TC is on the bench, I can't think of any way to say it's good. There's only one way to tell; by how it performs.You can cut it open and inspect the parts, and get a good idea of it's condition. But on the bench, about all you can tell is if the drive hub, and ring gear are ok .