th350 rear seal leak
I have a '77 and have had the same problem - I bought a 700 R$ and replaced 3 new seals and checked the run out. All was OK. It still leaked. The TCI guy ( sold me the 700R4) said the check my yoke. I didn't believe him but I just took it off and it has a small hole in the center of it!!!! The shaft seal is dry. Maybe you should check yours too. I amgoing to eposy the hole and see if it leaks too.
Good luck. Bill77C10
BTW - nice color on your truck- mine is almost exactly the same shade of blue -a custom Sikkens Color - go figure.