I had this same problem in my 727 right after I rebuilt it -- steady stream when driving -- turned out I nicked the front seal when installing it. Replaced the front seal, solved the problem.
I had swapped the original 273 out with a rebuilt one around 7 years ago and left the transmission In place. Bought a new front seal but didn’t replace it as the old one looked fine. Been driving for about 7 years and maybe 3-4K miles.
