I believe I had a 67 Dart GT convertible with the 273 4-bbl that had the fitting also. There should be a copper washer under the fitting that screws into the sector. I don't know if that is where yours is leaking, but mine leaked there until I got a new washer.
The funny thing about science is that if you change one miniscule parameter you change the entire outcome to the way you want it.
