727 transmission leak

I have Torqueflites come in for my $400 rebuild even tho they're shifting fine; just because they're leaking and they're tired of trying to find the leak. I replace every single seal and make sure there are absolutely no leaks whatsoever. I even have them bring the dipstick tube so I can install it myself. I don't want somebody jamming the tube in and nicking the o-ring. And they have to bring in the converter too; so I can check that to make sure it isn't worn or cracked.