I just finished developing the plates I made with the holders in question. I follow all the advice you gave me, and there is no leaks. Working carefully I found out that I'm the culprit, in my first take, when I turn the holder to make the second exposure, I realize that, even that it seemed that it was properly fitted, the holder wasn't fully seated on the inner rib, that needed an extra 1/16" to the end, leaving a small space that could produce the leaks.

I've learned a lesson here, I have to work with more attention on what I'm doing, don't take anything for granted.

Thanks folks.