The transfer port is not an issue in terms of "holding air", the only time it can leak is during firing.... Your most likely problem is that the valve is being held open because you reassembled the gun incorrectly.... It's been a while since I was inside a 140, but I do remember that there are a couple of parts that can go in either way and when installed incorrectly, the gun leaks air out as fast as you can pump it.... The other potential problem is the quad seal, but you say you replaced that....

AirGunEric is quite familiar with the 140, if he doesn't chime in, PM him....

Bob