I doubt an installation error Bronze Bird. I've done a couple before on my 68 without any problems. In fact when I restored the 69 about twenty years ago, it was done then without issues. It just started to leak one night out of the blue. First thing I tried was to put one of those special wrench's on it (I forget the name but they're like closed end wrenches that get a bite on more than two opposite sides. Have a little opening). and torque it down. Didn't stop it. That's when I figured the box was through... After the shock wore off on the recent rebuild failure, first thing I thought was a block somewhere as well Sleddog. It would have to be in the metal portion of the return line, (cause all other parts are new), but it checked out. I also thought about pressure but that would mean both pumps are acting up or maybe the wrong pulley. Unlikely though, I'm the 2nd owner of my 69 plus it was never an issue before... Bought a quick ratio Cardone. Flares looked good. I'll try your advise rohrt about backing off a few times. I also spoke with a f body guru out of state, and he said to crank that sucker down to the point of almost stripping it. Little worried about that advice but nothing else has worked. I appreciate all the input guys.