Hello all. I am not very well versed in the field of automatic trannies. My 1979 GMC 3500 454 t-400 will leak from the little tube at the top of the tranny when the truck is running and parked on a down slope. Level ground or upslope no leaking. Not running no leaking. When running the leak gets progressively worse with time. The tranny is a reman and doesn't have but mabey 5000k and 1000k of towing. Is this tube an overpressure relief? Why would it do this? Please use technical and layman terms to help.
Yhank you very much.